[coreboot] Re: Is there a way to enable a PCI-PCI bridge on bus 3 early?

[Keith Hui]

(Also including the list as I welcome more eyeballs.)

Hi Nico,

Thanks for your pointers.

On Fri, 22 Dec 2023 at 08:55, Nico Huber  wrote:
> Hi Keith,
>
> On 22.12.23 08:53, Keith Hui wrote:
> > My board has a PCI-PCI bridge on bus:device.func 3:0.0 (so bus 3, this
> > will be important) that services the PCI slot. After applying [1] to
> > have the PCH send port 80 data to PCI as I specified in Kconfig, I
> > still don't get any POST code... and not over LPC either, so I know my
> > patch works.
> >
> > Now I think I may need to enable CONFIG_EARLY_PCI_BRIDGE. Problem is
> > the bridge has to be a device on bus 0.
>
> you'll have to enable all bridges on the path to your PCI device.
> Starting with the bridge on bus 0. Note that all bus numbers except
> bus 0 are decided by software. The EARLY_PCI_BRIDGE code is currently
> not prepared for this. You'll have to
> configure more than one bus (repeat what the code currently does)
> configure PCI_SUBORDINATE_BUS everywhere to the highest bus number
> configure a port I/O range (code currently assumes MMIO)
> (I don't think there's a simple port 80h switch for PCI
>  bridges, but could be wrong)
>
> The code currently sets bus 15 (as a comment suggests, this is an
> arbitrary number >0). For your case with the P8Z77-M, the procedure
> could look like this:
>
> For 00:1c.6:
> PCI_SECONDARY_BUS    => 15
> PCI_SUBORDINATE_BUS  => 16
>
> For 0f:00.0:
> PCI_SECONDARY_BUS    => 16
> PCI_SUBORDINATE_BUS  => 16
>
> For both bridges:
> PCI_IO_BASE          => 0x00
> PCI_IO_LIMIT         => 0x00 (lower bits are implied to be 1s)
> PCI_IO_BASE_UPPER16  => 0x00 (registers only exist if indicated
> PCI_IO_LIMIT_UPPER16 => 0x00  by PCI_IO_BASE[0..3] == 0x01)
> PCI_COMMAND          => PCI_COMMAND_IO
>
> Then your device should show up as 10:00.0 (if the board uses
> 00 as slot number), in case you need to configure something there.
> That's usually done in pci_early_device_probe().

I came up with the code at the end of this email. However it renders
my board so inoperative I had to rescue myself. Can you see any
obvious errors in it?

I commented out the timeout part as I thought it was hanging me up. It was not.

Thanks
Keith

--------8<--------

void bootblock_mainboard_early_init(void)
{
    nuvoton_enable_serial(SERIAL_DEV, CONFIG_TTYS0_BASE);

if (CONFIG(POST_DEVICE_PCI_PCIE)) {
    /*
     * Enable PCIe root port 7 (00:1c.6) and the ASM1083 PCIe-PCI
bridge behind it
     * and have it accept I/O cycles. This should allow a POST card in
the PCI slot
     * to receive POST codes.
     *
     * Below is copied and modified from device/pci_early.c because
CONFIG_PCI_EARLY_BRIDGE
     * doesn't quite do what we need.
     */
        //int timeout;
        const int secondary = 3;
        pci_devfn_t bridge = PCH_PCIE_DEV(6);
        //pci_devfn_t p2p_bridge = PCI_DEV(secondary_bus, 0, 0);

/* Trigger secondary bus reset and program its bus number. */
        pci_s_assert_secondary_reset(bridge);
        pci_s_deassert_secondary_reset(bridge);
        pci_s_write_config8(bridge, PCI_SECONDARY_BUS, secondary);
        pci_s_write_config8(bridge, PCI_SUBORDINATE_BUS, secondary + 1);

u16 reg16;

/* Enable I/O window behind the bridge.
         * Base = 0x0000
         * Limit = 0x0FFF
         */
        pci_s_write_config16(bridge, PCI_IO_BASE, 0x0000);
        pci_or_config16(bridge, PCI_COMMAND, PCI_COMMAND_IO);

/* Enable subtractive decode (PECR3[SDE]). */
        pci_or_config8(bridge, 0xec, 0x01);
        /* Have to do it in D30F0 too, even though Z77 doesn't
natively do PCI. */
        pci_or_config32(PCI_DEV(0, 30, 0), 0x4c, (1 << 28));

/* Done with root port. Now do the 1083. */
        bridge = PCI_DEV(secondary, 0, 0);

/*        for (timeout = 20000; timeout; timeout--) {
            u32 id = pci_s_read_config32(bridge, PCI_VENDOR_ID);
            if (id != 0 && id != 0xffffffff && id != 0xffff0001)
                break;
            udelay(10);
        }*/

reg16 = pci_read_config16(bridge, PCI_CLASS_DEVICE);

if (reg16 != 0x0604)    /* PCI-PCI Bridge */
            return;

/* Trigger secondary bus reset and program its bus number. */
        pci_s_assert_secondary_reset(bridge);
        pci_s_deassert_secondary_reset(bridge);
        pci_s_write_config8(bridge, PCI_SECONDARY_BUS, secondary + 1);
        pci_s_write_config8(bridge, PCI_SUBORDINATE_BUS, secondary + 1);
        /* Set this second bridge to decode the same I/O ports. */
        pci_s_write_config16(bridge, PCI_IO_BASE, 0x0000);
        pci_or_config16(bridge, PCI_COMMAND, PCI_COMMAND_IO);
    }

}