[PATCH] pci: reserve resources for pcie-pci-bridge to fix regressed hotplug on q35 with ACPI hotplug enabled

[Igor Mammedov]

hotplug of a PCI device to empty at startup pcie-pci-bridge fails when
ACPI PCI hotplug (default since 6.1) is enabled due to lack of resources.
Reproduced with:

  #QEMU-6.2-rc1 -machine q35 -device pcie-pci-bridge,id=pcie-pci-bridge-0,addr=0x4

once linux guest is booted (test used Fedora 34), hotplug NIC from
QEMU monitor:
  (qemu) device_add rtl8139,bus=pcie-pci-bridge-0,addr=0x2

guest fails hotplug with:
  pci 0000:01:02.0: [10ec:8139] type 00 class 0x020000
  pci 0000:01:02.0: reg 0x10: [io  0x0000-0x00ff]
  pci 0000:01:02.0: reg 0x14: [mem 0x00000000-0x000000ff]
  pci 0000:01:02.0: reg 0x30: [mem 0x00000000-0x0003ffff pref]
  pci 0000:01:02.0: BAR 6: no space for [mem size 0x00040000 pref]
  pci 0000:01:02.0: BAR 6: failed to assign [mem size 0x00040000 pref]
  pci 0000:01:02.0: BAR 0: no space for [io  size 0x0100]
  pci 0000:01:02.0: BAR 0: failed to assign [io  size 0x0100]
  pci 0000:01:02.0: BAR 1: no space for [mem size 0x00000100]
  pci 0000:01:02.0: BAR 1: failed to assign [mem size 0x00000100]
  8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
  PCI Interrupt Link [GSIG] enabled at IRQ 22
  8139cp 0000:01:02.0: no MMIO resource
  8139cp: probe of 0000:01:02.0 failed with error -5

Reason for this is that commit [1] didn't take into account
pcie-pci-bridge, marking bridge as non hotpluggable instead of
handling it as possibly SHPC capable bridge.
Fix issue by checking if pcie-pci-bridge is SHPC capable and
if it is mark it as hotpluggable.

With this hotplug of rtl8139 succeeds, with caveat that it fail
initialize IO bar, which is caused by [2] which makes firmware
skip IO reservation for any PCI device which isn't correct in case
of pcie-pci-bridge.
Fix it by exposing hotplug type and making resource optional
only if PCIe hotplug is in use.

Fixes regression in QEMU-6.1 and later, since it's switched to ACPI
based PCI hotplug on Q35 by default at that time.

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2001732
[1]
Fixes: 3aa31d7d637 ("hw/pci: reserve IO and mem for pci express downstream ports with no devices attached")
[2]
Fixes: 76327b9f32a ("fw/pci: do not automatically allocate IO region for PCIe bridges")
Signed-off-by: Igor Mammedov <[e-mail]>
CC: [e-mail]
CC: [e-mail]
CC: [e-mail]
CC: [e-mail]
CC: [e-mail]
---
 src/fw/pciinit.c | 49 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 33 insertions(+), 16 deletions(-)

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index d25931bb..3107a0e6 100644
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -793,7 +793,13 @@ pci_region_create_entry(struct pci_bus *bus, struct pci_device *dev,
     return entry;
 }
 
-static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
+typedef enum hotplug_type_t {
+    HOTPLUG_NO_SUPPORTED = 0,
+    HOTPLUG_PCIE,
+    HOTPLUG_SHPC
+} hotplug_type_t;
+
+static hotplug_type_t pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
 {
     u8 shpc_cap;
 
@@ -804,22 +810,31 @@ static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
                        (__builtin_ffs(PCI_EXP_FLAGS_TYPE) - 1));
         u8 downstream_port = (port_type == PCI_EXP_TYPE_DOWNSTREAM) ||
                              (port_type == PCI_EXP_TYPE_ROOT_PORT);
-        /*
-         * PCI Express SPEC, 7.8.2:
-         *   Slot Implemented – When Set, this bit indicates that the Link
-         *   HwInit associated with this Port is connected to a slot (as
-         *   compared to being connected to a system-integrated device or
-         *   being disabled).
-         *   This bit is valid for Downstream Ports. This bit is undefined
-         *   for Upstream Ports.
-         */
-        u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
-
-        return downstream_port && slot_implemented;
+
+        switch (port_type) {
+            case PCI_EXP_TYPE_PCI_BRIDGE:
+                /* fall-through to check if SHPC is enabled on bridge */
+                break;
+            default: {
+                /*
+                 * PCI Express SPEC, 7.8.2:
+                 *   Slot Implemented – When Set, this bit indicates that the Link
+                 *   HwInit associated with this Port is connected to a slot (as
+                 *   compared to being connected to a system-integrated device or
+                 *   being disabled).
+                 *   This bit is valid for Downstream Ports. This bit is undefined
+                 *   for Upstream Ports.
+                 */
+                 u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
+                 return downstream_port && slot_implemented ?
+                     HOTPLUG_PCIE : HOTPLUG_NO_SUPPORTED;
+                 break;
+            }
+        }
     }
 
     shpc_cap = pci_find_capability(bus->bus_dev->bdf, PCI_CAP_ID_SHPC, 0);
-    return !!shpc_cap;
+    return !!shpc_cap ? HOTPLUG_SHPC : HOTPLUG_NO_SUPPORTED;
 }
 
 /* Test whether bridge support forwarding of transactions
@@ -904,7 +919,7 @@ static int pci_bios_check_devices(struct pci_bus *busses)
         u8 pcie_cap = pci_find_capability(bdf, PCI_CAP_ID_EXP, 0);
         u8 qemu_cap = pci_find_resource_reserve_capability(bdf);
 
-        int hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
+        hotplug_type_t hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
         for (type = 0; type < PCI_REGION_TYPE_COUNT; type++) {
             u64 align = (type == PCI_REGION_TYPE_IO) ?
                 PCI_BRIDGE_IO_MIN : PCI_BRIDGE_MEM_MIN;
@@ -948,7 +963,9 @@ static int pci_bios_check_devices(struct pci_bus *busses)
             if (pci_region_align(&s->r[type]) > align)
                  align = pci_region_align(&s->r[type]);
             u64 sum = pci_region_sum(&s->r[type]);
-            int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
+            int resource_optional = 0;
+            if (hotplug_support == HOTPLUG_PCIE)
+                resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
             if (!sum && hotplug_support && !resource_optional)
                 sum = align; /* reserve min size for hot-plug */
             if (size > sum) {
-- 
2.27.0

[Paul Menzel]

Dear Igor,


Am 26.11.21 um 19:46 schrieb Igor Mammedov:
> hotplug of a PCI device to empty at startup pcie-pci-bridge fails when

“to empty”, what does that mean?
> ACPI PCI hotplug (default since 6.1) is enabled due to lack of resources.

QEMU 6.1?
> Reproduced with:
>
> #QEMU-6.2-rc1 -machine q35 -device pcie-pci-bridge,id=pcie-pci-bridge-0,addr=0x4
>
> once linux guest is booted (test used Fedora 34), hotplug NIC from
> QEMU monitor:
>    (qemu) device_add rtl8139,bus=pcie-pci-bridge-0,addr=0x2
>
> guest fails hotplug with:
>    pci 0000:01:02.0: [10ec:8139] type 00 class 0x020000
>    pci 0000:01:02.0: reg 0x10: [io  0x0000-0x00ff]
>    pci 0000:01:02.0: reg 0x14: [mem 0x00000000-0x000000ff]
>    pci 0000:01:02.0: reg 0x30: [mem 0x00000000-0x0003ffff pref]
>    pci 0000:01:02.0: BAR 6: no space for [mem size 0x00040000 pref]
>    pci 0000:01:02.0: BAR 6: failed to assign [mem size 0x00040000 pref]
>    pci 0000:01:02.0: BAR 0: no space for [io  size 0x0100]
>    pci 0000:01:02.0: BAR 0: failed to assign [io  size 0x0100]
>    pci 0000:01:02.0: BAR 1: no space for [mem size 0x00000100]
>    pci 0000:01:02.0: BAR 1: failed to assign [mem size 0x00000100]
>    8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
>    PCI Interrupt Link [GSIG] enabled at IRQ 22
>    8139cp 0000:01:02.0: no MMIO resource
>    8139cp: probe of 0000:01:02.0 failed with error -5
>
> Reason for this is that commit [1] didn't take into account
> pcie-pci-bridge, marking bridge as non hotpluggable instead of
> handling it as possibly SHPC capable bridge.
> Fix issue by checking if pcie-pci-bridge is SHPC capable and
> if it is mark it as hotpluggable.
>
> With this hotplug of rtl8139 succeeds, with caveat that it fail

Nit: fail*s* *to*
> initialize IO bar, which is caused by [2] which makes firmware
> skip IO reservation for any PCI device which isn't correct in case
> of pcie-pci-bridge.
> Fix it by exposing hotplug type and making resource optional
> only if PCIe hotplug is in use.
>
> Fixes regression in QEMU-6.1 and later, since it's switched to ACPI

Nit: was switched
> based PCI hotplug on Q35 by default at that time.
>
> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2001732
> [1]
> Fixes: 3aa31d7d637 ("hw/pci: reserve IO and mem for pci express downstream ports with no devices attached")
> [2]
> Fixes: 76327b9f32a ("fw/pci: do not automatically allocate IO region for PCIe bridges")
> Signed-off-by: Igor Mammedov <[e-mail]>
> CC: [e-mail]
> CC: [e-mail]
> CC: [e-mail]
> CC: [e-mail]
> CC: [e-mail]
> ---
>   src/fw/pciinit.c | 49 ++++++++++++++++++++++++++++++++----------------
>   1 file changed, 33 insertions(+), 16 deletions(-)
>
> diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> index d25931bb..3107a0e6 100644
> --- a/src/fw/pciinit.c
> +++ b/src/fw/pciinit.c
> @@ -793,7 +793,13 @@ pci_region_create_entry(struct pci_bus *bus, struct pci_device *dev,
>       return entry;
>   }
>
> -static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> +typedef enum hotplug_type_t {
> +    HOTPLUG_NO_SUPPORTED = 0,
> +    HOTPLUG_PCIE,
> +    HOTPLUG_SHPC
> +} hotplug_type_t;
> +
> +static hotplug_type_t pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
>   {
>       u8 shpc_cap;
>
> @@ -804,22 +810,31 @@ static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
>                          (__builtin_ffs(PCI_EXP_FLAGS_TYPE) - 1));
>           u8 downstream_port = (port_type == PCI_EXP_TYPE_DOWNSTREAM) ||
>                                (port_type == PCI_EXP_TYPE_ROOT_PORT);
> -        /*
> -         * PCI Express SPEC, 7.8.2:
> -         *   Slot Implemented – When Set, this bit indicates that the Link
> -         *   HwInit associated with this Port is connected to a slot (as
> -         *   compared to being connected to a system-integrated device or
> -         *   being disabled).
> -         *   This bit is valid for Downstream Ports. This bit is undefined
> -         *   for Upstream Ports.
> -         */
> -        u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
> -
> -        return downstream_port && slot_implemented;
> +
> +        switch (port_type) {
> +            case PCI_EXP_TYPE_PCI_BRIDGE:
> +                /* fall-through to check if SHPC is enabled on bridge */

Doesn’t fall-through for switch statements mean, there is no break 
statement?
> +                break;
> +            default: {
> +                /*
> +                 * PCI Express SPEC, 7.8.2:
> +                 *   Slot Implemented – When Set, this bit indicates that the Link
> +                 *   HwInit associated with this Port is connected to a slot (as
> +                 *   compared to being connected to a system-integrated device or
> +                 *   being disabled).
> +                 *   This bit is valid for Downstream Ports. This bit is undefined
> +                 *   for Upstream Ports.
> +                 */
> +                 u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
> +                 return downstream_port && slot_implemented ?
> +                     HOTPLUG_PCIE : HOTPLUG_NO_SUPPORTED;
> +                 break;
> +            }
> +        }
>       }
>
> shpc_cap = pci_find_capability(bus->bus_dev->bdf, PCI_CAP_ID_SHPC, 0);
> -    return !!shpc_cap;
> +    return !!shpc_cap ? HOTPLUG_SHPC : HOTPLUG_NO_SUPPORTED;
>   }
>
> /* Test whether bridge support forwarding of transactions
> @@ -904,7 +919,7 @@ static int pci_bios_check_devices(struct pci_bus *busses)
>           u8 pcie_cap = pci_find_capability(bdf, PCI_CAP_ID_EXP, 0);
>           u8 qemu_cap = pci_find_resource_reserve_capability(bdf);
>
> -        int hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
> +        hotplug_type_t hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
>           for (type = 0; type < PCI_REGION_TYPE_COUNT; type++) {
>               u64 align = (type == PCI_REGION_TYPE_IO) ?
>                   PCI_BRIDGE_IO_MIN : PCI_BRIDGE_MEM_MIN;
> @@ -948,7 +963,9 @@ static int pci_bios_check_devices(struct pci_bus *busses)
>               if (pci_region_align(&s->r[type]) > align)
>                    align = pci_region_align(&s->r[type]);
>               u64 sum = pci_region_sum(&s->r[type]);
> -            int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
> +            int resource_optional = 0;
> +            if (hotplug_support == HOTPLUG_PCIE)
> +                resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
>               if (!sum && hotplug_support && !resource_optional)
>                   sum = align; /* reserve min size for hot-plug */
>               if (size > sum) {

Rest looks good.


Kind regards,

Paul

[Igor Mammedov]

On Sat, 27 Nov 2021 11:19:35 +0100
Paul Menzel <[e-mail]> wrote:
> Dear Igor,
>
> Am 26.11.21 um 19:46 schrieb Igor Mammedov:
> > hotplug of a PCI device to empty at startup pcie-pci-bridge fails when
>
> “to empty”, what does that mean?

meaning is pcie-pci-bridge that does not have any devices plugged into it.
maybe 'not populated' would be more clear?
> > ACPI PCI hotplug (default since 6.1) is enabled due to lack of resources.
>
> QEMU 6.1?
> > Reproduced with:
> >
> > #QEMU-6.2-rc1 -machine q35 -device pcie-pci-bridge,id=pcie-pci-bridge-0,addr=0x4
> >
> > once linux guest is booted (test used Fedora 34), hotplug NIC from
> > QEMU monitor:
> >    (qemu) device_add rtl8139,bus=pcie-pci-bridge-0,addr=0x2
> >
> > guest fails hotplug with:
> >    pci 0000:01:02.0: [10ec:8139] type 00 class 0x020000
> >    pci 0000:01:02.0: reg 0x10: [io  0x0000-0x00ff]
> >    pci 0000:01:02.0: reg 0x14: [mem 0x00000000-0x000000ff]
> >    pci 0000:01:02.0: reg 0x30: [mem 0x00000000-0x0003ffff pref]
> >    pci 0000:01:02.0: BAR 6: no space for [mem size 0x00040000 pref]
> >    pci 0000:01:02.0: BAR 6: failed to assign [mem size 0x00040000 pref]
> >    pci 0000:01:02.0: BAR 0: no space for [io  size 0x0100]
> >    pci 0000:01:02.0: BAR 0: failed to assign [io  size 0x0100]
> >    pci 0000:01:02.0: BAR 1: no space for [mem size 0x00000100]
> >    pci 0000:01:02.0: BAR 1: failed to assign [mem size 0x00000100]
> >    8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
> >    PCI Interrupt Link [GSIG] enabled at IRQ 22
> >    8139cp 0000:01:02.0: no MMIO resource
> >    8139cp: probe of 0000:01:02.0 failed with error -5
> >
> > Reason for this is that commit [1] didn't take into account
> > pcie-pci-bridge, marking bridge as non hotpluggable instead of
> > handling it as possibly SHPC capable bridge.
> > Fix issue by checking if pcie-pci-bridge is SHPC capable and
> > if it is mark it as hotpluggable.
> >
> > With this hotplug of rtl8139 succeeds, with caveat that it fail
>
> Nit: fail*s* *to*
> > initialize IO bar, which is caused by [2] which makes firmware
> > skip IO reservation for any PCI device which isn't correct in case
> > of pcie-pci-bridge.
> > Fix it by exposing hotplug type and making resource optional
> > only if PCIe hotplug is in use.
> >
> > Fixes regression in QEMU-6.1 and later, since it's switched to ACPI
>
> Nit: was switched
> > based PCI hotplug on Q35 by default at that time.
> >
> > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2001732
> > [1]
> > Fixes: 3aa31d7d637 ("hw/pci: reserve IO and mem for pci express downstream ports with no devices attached")
> > [2]
> > Fixes: 76327b9f32a ("fw/pci: do not automatically allocate IO region for PCIe bridges")
> > Signed-off-by: Igor Mammedov <[e-mail]>
> > CC: [e-mail]
> > CC: [e-mail]
> > CC: [e-mail]
> > CC: [e-mail]
> > CC: [e-mail]
> > ---
> >   src/fw/pciinit.c | 49 ++++++++++++++++++++++++++++++++----------------
> >   1 file changed, 33 insertions(+), 16 deletions(-)
> >
> > diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> > index d25931bb..3107a0e6 100644
> > --- a/src/fw/pciinit.c
> > +++ b/src/fw/pciinit.c
> > @@ -793,7 +793,13 @@ pci_region_create_entry(struct pci_bus *bus, struct pci_device *dev,
> >       return entry;
> >   }
> >
> > -static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> > +typedef enum hotplug_type_t {
> > +    HOTPLUG_NO_SUPPORTED = 0,
> > +    HOTPLUG_PCIE,
> > +    HOTPLUG_SHPC
> > +} hotplug_type_t;
> > +
> > +static hotplug_type_t pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> >   {
> >       u8 shpc_cap;
> >
> > @@ -804,22 +810,31 @@ static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> >                          (__builtin_ffs(PCI_EXP_FLAGS_TYPE) - 1));
> >           u8 downstream_port = (port_type == PCI_EXP_TYPE_DOWNSTREAM) ||
> >                                (port_type == PCI_EXP_TYPE_ROOT_PORT);
> > -        /*
> > -         * PCI Express SPEC, 7.8.2:
> > -         *   Slot Implemented – When Set, this bit indicates that the Link
> > -         *   HwInit associated with this Port is connected to a slot (as
> > -         *   compared to being connected to a system-integrated device or
> > -         *   being disabled).
> > -         *   This bit is valid for Downstream Ports. This bit is undefined
> > -         *   for Upstream Ports.
> > -         */
> > -        u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
> > -
> > -        return downstream_port && slot_implemented;
> > +
> > +        switch (port_type) {
> > +            case PCI_EXP_TYPE_PCI_BRIDGE:
> > +                /* fall-through to check if SHPC is enabled on bridge */
>
> Doesn’t fall-through for switch statements mean, there is no break 
> statement?

how about
 /* do nothing and check later if SHPC is enabled */
> > +                break;
> > +            default: {
> > +                /*
> > +                 * PCI Express SPEC, 7.8.2:
> > +                 *   Slot Implemented – When Set, this bit indicates that the Link
> > +                 *   HwInit associated with this Port is connected to a slot (as
> > +                 *   compared to being connected to a system-integrated device or
> > +                 *   being disabled).
> > +                 *   This bit is valid for Downstream Ports. This bit is undefined
> > +                 *   for Upstream Ports.
> > +                 */
> > +                 u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
> > +                 return downstream_port && slot_implemented ?
> > +                     HOTPLUG_PCIE : HOTPLUG_NO_SUPPORTED;
> > +                 break;
> > +            }
> > +        }
> >       }
> >
> > shpc_cap = pci_find_capability(bus->bus_dev->bdf, PCI_CAP_ID_SHPC, 0);
> > -    return !!shpc_cap;
> > +    return !!shpc_cap ? HOTPLUG_SHPC : HOTPLUG_NO_SUPPORTED;
> >   }
> >
> > /* Test whether bridge support forwarding of transactions
> > @@ -904,7 +919,7 @@ static int pci_bios_check_devices(struct pci_bus *busses)
> >           u8 pcie_cap = pci_find_capability(bdf, PCI_CAP_ID_EXP, 0);
> >           u8 qemu_cap = pci_find_resource_reserve_capability(bdf);
> >
> > -        int hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
> > +        hotplug_type_t hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
> >           for (type = 0; type < PCI_REGION_TYPE_COUNT; type++) {
> >               u64 align = (type == PCI_REGION_TYPE_IO) ?
> >                   PCI_BRIDGE_IO_MIN : PCI_BRIDGE_MEM_MIN;
> > @@ -948,7 +963,9 @@ static int pci_bios_check_devices(struct pci_bus *busses)
> >               if (pci_region_align(&s->r[type]) > align)
> >                    align = pci_region_align(&s->r[type]);
> >               u64 sum = pci_region_sum(&s->r[type]);
> > -            int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
> > +            int resource_optional = 0;
> > +            if (hotplug_support == HOTPLUG_PCIE)
> > +                resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
> >               if (!sum && hotplug_support && !resource_optional)
> >                   sum = align; /* reserve min size for hot-plug */
> >               if (size > sum) {
>
> Rest looks good.
>
> Kind regards,
>
> Paul

[Paul Menzel]

Dear Igor,


Am 27.11.21 um 12:16 schrieb Igor Mammedov:
> On Sat, 27 Nov 2021 11:19:35 +0100 wrote:
> > Am 26.11.21 um 19:46 schrieb Igor Mammedov:
> > > hotplug of a PCI device to empty at startup pcie-pci-bridge fails when
> >
> > “to empty”, what does that mean?
>
> meaning is pcie-pci-bridge that does not have any devices plugged into it.
> maybe 'not populated' would be more clear?

Ah, the “at startup“ confused me then. Maybe (but I am no native speaker):

Hotplugging a PCI device to a since startup unpopulated pcee-pci-bridge 
fails …
> > > ACPI PCI hotplug (default since 6.1) is enabled due to lack of resources.
> >
> > QEMU 6.1?
> > > Reproduced with:
> > >
> > > #QEMU-6.2-rc1 -machine q35 -device pcie-pci-bridge,id=pcie-pci-bridge-0,addr=0x4
> > >
> > > once linux guest is booted (test used Fedora 34), hotplug NIC from
> > > QEMU monitor:
> > >     (qemu) device_add rtl8139,bus=pcie-pci-bridge-0,addr=0x2
> > >
> > > guest fails hotplug with:
> > >     pci 0000:01:02.0: [10ec:8139] type 00 class 0x020000
> > >     pci 0000:01:02.0: reg 0x10: [io  0x0000-0x00ff]
> > >     pci 0000:01:02.0: reg 0x14: [mem 0x00000000-0x000000ff]
> > >     pci 0000:01:02.0: reg 0x30: [mem 0x00000000-0x0003ffff pref]
> > >     pci 0000:01:02.0: BAR 6: no space for [mem size 0x00040000 pref]
> > >     pci 0000:01:02.0: BAR 6: failed to assign [mem size 0x00040000 pref]
> > >     pci 0000:01:02.0: BAR 0: no space for [io  size 0x0100]
> > >     pci 0000:01:02.0: BAR 0: failed to assign [io  size 0x0100]
> > >     pci 0000:01:02.0: BAR 1: no space for [mem size 0x00000100]
> > >     pci 0000:01:02.0: BAR 1: failed to assign [mem size 0x00000100]
> > >     8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
> > >     PCI Interrupt Link [GSIG] enabled at IRQ 22
> > >     8139cp 0000:01:02.0: no MMIO resource
> > >     8139cp: probe of 0000:01:02.0 failed with error -5
> > >
> > > Reason for this is that commit [1] didn't take into account
> > > pcie-pci-bridge, marking bridge as non hotpluggable instead of
> > > handling it as possibly SHPC capable bridge.
> > > Fix issue by checking if pcie-pci-bridge is SHPC capable and
> > > if it is mark it as hotpluggable.
> > >
> > > With this hotplug of rtl8139 succeeds, with caveat that it fail
> >
> > Nit: fail*s* *to*
> > > initialize IO bar, which is caused by [2] which makes firmware
> > > skip IO reservation for any PCI device which isn't correct in case
> > > of pcie-pci-bridge.
> > > Fix it by exposing hotplug type and making resource optional
> > > only if PCIe hotplug is in use.
> > >
> > > Fixes regression in QEMU-6.1 and later, since it's switched to ACPI
> >
> > Nit: was switched
> > > based PCI hotplug on Q35 by default at that time.
> > >
> > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2001732
> > > [1]
> > > Fixes: 3aa31d7d637 ("hw/pci: reserve IO and mem for pci express downstream ports with no devices attached")
> > > [2]
> > > Fixes: 76327b9f32a ("fw/pci: do not automatically allocate IO region for PCIe bridges")
> > > Signed-off-by: Igor Mammedov <[e-mail]>
> > > CC: [e-mail]
> > > CC: [e-mail]
> > > CC: [e-mail]
> > > CC: [e-mail]
> > > CC: [e-mail]
> > > ---
> > >    src/fw/pciinit.c | 49 ++++++++++++++++++++++++++++++++----------------
> > >    1 file changed, 33 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> > > index d25931bb..3107a0e6 100644
> > > --- a/src/fw/pciinit.c
> > > +++ b/src/fw/pciinit.c
> > > @@ -793,7 +793,13 @@ pci_region_create_entry(struct pci_bus *bus, struct pci_device *dev,
> > >        return entry;
> > >    }
> > >
> > > -static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> > > +typedef enum hotplug_type_t {
> > > +    HOTPLUG_NO_SUPPORTED = 0,
> > > +    HOTPLUG_PCIE,
> > > +    HOTPLUG_SHPC
> > > +} hotplug_type_t;
> > > +
> > > +static hotplug_type_t pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> > >    {
> > >        u8 shpc_cap;
> > >
> > > @@ -804,22 +810,31 @@ static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
> > >                           (__builtin_ffs(PCI_EXP_FLAGS_TYPE) - 1));
> > >            u8 downstream_port = (port_type == PCI_EXP_TYPE_DOWNSTREAM) ||
> > >                                 (port_type == PCI_EXP_TYPE_ROOT_PORT);
> > > -        /*
> > > -         * PCI Express SPEC, 7.8.2:
> > > -         *   Slot Implemented – When Set, this bit indicates that the Link
> > > -         *   HwInit associated with this Port is connected to a slot (as
> > > -         *   compared to being connected to a system-integrated device or
> > > -         *   being disabled).
> > > -         *   This bit is valid for Downstream Ports. This bit is undefined
> > > -         *   for Upstream Ports.
> > > -         */
> > > -        u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
> > > -
> > > -        return downstream_port && slot_implemented;
> > > +
> > > +        switch (port_type) {
> > > +            case PCI_EXP_TYPE_PCI_BRIDGE:
> > > +                /* fall-through to check if SHPC is enabled on bridge */
> >
> > Doesn’t fall-through for switch statements mean, there is no break
> > statement?
>
> how about
>   /* do nothing and check later if SHPC is enabled */

Sounds good.


Kind regards,

Paul
> > > +                break;
> > > +            default: {
> > > +                /*
> > > +                 * PCI Express SPEC, 7.8.2:
> > > +                 *   Slot Implemented – When Set, this bit indicates that the Link
> > > +                 *   HwInit associated with this Port is connected to a slot (as
> > > +                 *   compared to being connected to a system-integrated device or
> > > +                 *   being disabled).
> > > +                 *   This bit is valid for Downstream Ports. This bit is undefined
> > > +                 *   for Upstream Ports.
> > > +                 */
> > > +                 u16 slot_implemented = pcie_flags & PCI_EXP_FLAGS_SLOT;
> > > +                 return downstream_port && slot_implemented ?
> > > +                     HOTPLUG_PCIE : HOTPLUG_NO_SUPPORTED;
> > > +                 break;
> > > +            }
> > > +        }
> > >        }
> > >
> > > shpc_cap = pci_find_capability(bus->bus_dev->bdf, PCI_CAP_ID_SHPC, 0);
> > > -    return !!shpc_cap;
> > > +    return !!shpc_cap ? HOTPLUG_SHPC : HOTPLUG_NO_SUPPORTED;
> > >    }
> > >
> > > /* Test whether bridge support forwarding of transactions
> > > @@ -904,7 +919,7 @@ static int pci_bios_check_devices(struct pci_bus *busses)
> > >            u8 pcie_cap = pci_find_capability(bdf, PCI_CAP_ID_EXP, 0);
> > >            u8 qemu_cap = pci_find_resource_reserve_capability(bdf);
> > >
> > > -        int hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
> > > +        hotplug_type_t hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
> > >            for (type = 0; type < PCI_REGION_TYPE_COUNT; type++) {
> > >                u64 align = (type == PCI_REGION_TYPE_IO) ?
> > >                    PCI_BRIDGE_IO_MIN : PCI_BRIDGE_MEM_MIN;
> > > @@ -948,7 +963,9 @@ static int pci_bios_check_devices(struct pci_bus *busses)
> > >                if (pci_region_align(&s->r[type]) > align)
> > >                     align = pci_region_align(&s->r[type]);
> > >                u64 sum = pci_region_sum(&s->r[type]);
> > > -            int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
> > > +            int resource_optional = 0;
> > > +            if (hotplug_support == HOTPLUG_PCIE)
> > > +                resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
> > >                if (!sum && hotplug_support && !resource_optional)
> > >                    sum = align; /* reserve min size for hot-plug */
> > >                if (size > sum) {