Re: [SeaBIOS] [PATCH] pci: add RedHat PCI BRIDGE capability

[Liu, Jing2]

On 8/7/2018 7:43 PM, Laszlo Ersek wrote:
> adding Marcel; comments at the bottom
>
> On 08/07/18 09:20, Jing Liu wrote:
> > Add a device-specific capability for the RedHat PCI BRIDGE
> > to enable reserving additional resources.
> > Signed-off-by: Jing Liu
> >
> > src/fw/pciinit.c | 9 ++++++---
> >   src/hw/pci_ids.h | 1 +
> >   2 files changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
> > index 3a2f747..0265e9d 100644
> > --- a/src/fw/pciinit.c
> > +++ b/src/fw/pciinit.c
> > @@ -525,9 +525,12 @@ static void pci_bios_init_platform(void)
> >
> > static u8 pci_find_resource_reserve_capability(u16 bdf)
> >   {
> > if (pci_config_readw(bdf, PCI_VENDOR_ID) == PCI_VENDOR_ID_REDHAT &&
> >    pci_config_readw(bdf, PCI_DEVICE_ID) ==
> >            PCI_DEVICE_ID_REDHAT_ROOT_PORT) {
> > u16 vendor_id = pci_config_readw(bdf, PCI_VENDOR_ID);
> > u16 device_id = pci_config_readw(bdf, PCI_DEVICE_ID);
> > if (vendor_id == PCI_VENDOR_ID_REDHAT &&
> >    (device_id == PCI_DEVICE_ID_REDHAT_ROOT_PORT ||
> >     device_id == PCI_DEVICE_ID_REDHAT_BRIDGE)) {
> >     u8 cap = 0;
> >     do {
> >         cap = pci_find_capability(bdf, PCI_CAP_ID_VNDR, cap);
> >
> > diff --git a/src/hw/pci_ids.h b/src/hw/pci_ids.h
> > index 38fa2ca..1096461 100644
> > --- a/src/hw/pci_ids.h
> > +++ b/src/hw/pci_ids.h
> > @@ -2265,6 +2265,7 @@
> >
> > #define PCI_VENDOR_ID_REDHAT		0x1b36
> >   #define PCI_DEVICE_ID_REDHAT_ROOT_PORT	0x000C
> > +#define PCI_DEVICE_ID_REDHAT_BRIDGE	0x0001
> >
> > #define PCI_VENDOR_ID_TEKRAM		0x1de1
> >   #define PCI_DEVICE_ID_TEKRAM_DC290	0xdc29
>
> Given that you are touching this function, it's a good opportunity to
> clean up its issues that I pointed out earlier in
> https://bugzilla.redhat.com/show_bug.cgi?id=1536147#c0, noted as "side
> comments (a), (b) and (c)". I'll re-iterate:
>
> The "PCI: QEMU resource reserve cap not found" debug message is
>  printed under wrong conditions. Namely, it is both printed when it
>  makes no sense (i.e., when the vendor-id/device-id don't match and we
>  don't even go looking for the capability), and it's *not* printed when
>  it does makes sense (the search loop completes without finding the
>  capability).
>
> There is a logic bug: if we find the capability but it's truncated, we
>  print a good error message, but then go ahead and return the offset of
>  the broken (truncated) capability just the same. In this case, we
>  should return zero.

I agree with you!
> So, I suggest that you please:
>
> (1) send a patch that fixes the logic bug,
>
> (2) send another patch that cleans up the debug messages,
>
> (3) send yet another patch that recognizes the capability in question on
>      the traditional bridge device too. (I.e., a variant of the current
>      patch, rebased to (1) and (2)).

I will prepare these patches and welcome comments.
> More comments for this patch:
>
> (4) the subject line should be clarified, such as:
>    pci: recognize RH resource reservation capability on traditional bridges
>
>  (72 characters). The commit message body should be updated
>  accordingly -- we're not adding the capability, just matching it on
>  another device.

Got it, change the title and commit message later.
> (5) Regarding the code: I'm not sure how careful SeaBIOS is about
>      unnecessary config space accesses (i.e., unnecessary traps to the
>      host). Personally I would prefer if we didn't unconditionally read
>      the device ID post-patch either -- that is, if the vendor ID doesn't
>      match, we shouldn't read the device ID. Something like:

Do you mean we need prevent the compiler read device ID in advanced when
vendor ID does not matched?
If not, why the original codes will read device ID when the vendor Id
check fails?
> > u16 device_id;
> >
> > if (pci_config_readw(bdf, PCI_VENDOR_ID) != PCI_VENDOR_ID_REDHAT) {
> >      return 0;
> >    }
> >
> > device_id = pci_config_readw(bdf, PCI_DEVICE_ID);
> >    if (device_id != PCI_DEVICE_ID_REDHAT_ROOT_PORT &&
> >        device_id != PCI_DEVICE_ID_REDHAT_BRIDGE) {
> >      return 0;
> >    }
> >
> > /* success / failure messages are justified after this point */
> >    ...
>
> The vendor-id/device-id checks should likely be reorganized as shown
> above in patch (2), as a part of the debug message cleanup. And then the
> device-id check can be extended to cover PCI_DEVICE_ID_REDHAT_BRIDGE in
> patch (3).
>
> Just my opinion of course; I'm not a SeaBIOS maintainer.

Thank you very much, Laszlo!
Jing
> Thanks,
> Laszlo