Re: [edk2-devel] [PATCH] Ovmf: Set matching PCI routing values in PIIX4

["Laszlo Ersek" <lersek@redhat.com>]

On 12/08/20 15:51, Borghorst, Hendrik via groups.io wrote:
> The OVMF package tries to mimic the PCI initialization of SeaBIOS.
> Both set the PCI_INTERRUPT_LINE register according to the same
> logic with rotation based on IRQs (10, 10, 11, 11). However, while
> SeaBIOS applies these IRQs to the PCI interrupt routing register (0x60)
> of the PIIX4, OVMF wrongly applies (11, 11, 10, 10) which breaks legacy
> INTx routing.
>
> Signed-off-by: Hendrik Borghorst <hborghor@amazon.de>
> Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>  .../PlatformBootManagerLib/BdsPlatform.c      | 24 +++++++++----------
>  1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/OvmfPkg/Library/PlatformBootManagerLib/BdsPlatform.c b/OvmfPkg/Library/PlatformBootManagerLib/BdsPlatform.c
> index 3c55ec9bd9..b8c3f54be6 100644
> --- a/OvmfPkg/Library/PlatformBootManagerLib/BdsPlatform.c
> +++ b/OvmfPkg/Library/PlatformBootManagerLib/BdsPlatform.c
> @@ -1211,24 +1211,24 @@ PciAcpiInitialization (
>        //
>        // 00:01.0 ISA Bridge (PIIX4) LNK routing targets
>        //
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x60), 0x0b); // A
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x61), 0x0b); // B
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x62), 0x0a); // C
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x63), 0x0a); // D
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x60), PciHostIrqs[0]); // A
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x61), PciHostIrqs[1]); // B
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x62), PciHostIrqs[2]); // C
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 1, 0, 0x63), PciHostIrqs[3]); // D
>        break;
>      case INTEL_Q35_MCH_DEVICE_ID:
>        Pmba = POWER_MGMT_REGISTER_Q35 (ICH9_PMBASE);
>        //
>        // 00:1f.0 LPC Bridge (Q35) LNK routing targets
>        //
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x60), 0x0a); // A
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x61), 0x0a); // B
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x62), 0x0b); // C
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x63), 0x0b); // D
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x68), 0x0a); // E
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x69), 0x0a); // F
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x6a), 0x0b); // G
> -      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x6b), 0x0b); // H
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x60), PciHostIrqs[0]); // A
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x61), PciHostIrqs[1]); // B
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x62), PciHostIrqs[2]); // C
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x63), PciHostIrqs[3]); // D
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x68), PciHostIrqs[0]); // E
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x69), PciHostIrqs[1]); // F
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x6a), PciHostIrqs[2]); // G
> +      PciWrite8 (PCI_LIB_ADDRESS (0, 0x1f, 0, 0x6b), PciHostIrqs[3]); // H
>        break;
>      default:
>        if (XenDetected ()) {
>

The patch is correct, in my opinion; the commit message is lacking.

(1) The rotating pattern is a map:

  (slot, function) --> (interrupt link) [LNKA..LNKD]

(more precisely, it is a pattern from (slot, pin) to (interrupt link),
but function<->pin is an identity mapping in the QEMU hardware, so we
can just use (slot, function) rather than (slot, pin) on the left hand
side. But I digress.)

The ACPI _PRT object is generated by QEMU; it describes this map.

(2) Another map is

  (interrupt link) --> { set of possible interrupt numbers,
                         for this link }

This map is given by the LNK[A..D] ACPI objects, also given by QEMU.

(3) What the firmware is expected to do is:

(3a) for each interrupt link, select an *actual* interrupt from the set
that's possible for that link, yielding a deterministic map

  (interrupt link) --> (actual interrupt number)

and

(3b) for each PCI device/function with an interrupt pin, resolve the

  (slot, function) --> (interrupt link) --> (actual interrupt number)

functional composition, and program the result into the Interrupt Line
register of the device.

In OVMF, we do not parse the rotating map described under (1) from
QEMU's _PRT object. Instead, we duplicate the code. This is not a
problem.

In OVMF, we also do not parse the map described under (2) from QEMU's
ACPI content. Instead, we pick a specific selection (3a) that we
"apriori" know satisfies (2). This is also not a problem. OVMF's
particular selection is the PciHostIrqs table.

(

Table (2) from QEMU is

  LNKA -> { 5, 10, 11 }
  LNKB -> { 5, 10, 11 }
  LNKC -> { 5, 10, 11 }
  LNKD -> { 5, 10, 11 }

and our specific pick in OVMF, in the PciHostIrqs table, is

  LNKA -> 10
  LNKB -> 10
  LNKC -> 11
  LNKD -> 11

)

In OVMF, we also cover step (3b), in the SetPciIntLine() function.

What's missing in OVMF -- and what this patch corrects -- is that we
currently fail to program our selection for table (3) into the hardware.
We pick a specific LNKx->IRQ# mapping for each interrupt link, and we
correctly program the PCI Interrupt Line registers through those
link-to-IRQ mappings -- but we don't tell the hardware about the
link-to-IRQ mappings. More precisely, we program such a link-to-IRQ
mapping table into the hardware that is then not matched by the mapping
we use for programming the PCI device/function interrupt lines. As a
result, some PCI Interrupt Line registers will have impossible values --
a given (slot, function) may use a particular link, but also report an
interrupt number that was never picked for that link.


Please submit v2 of this patch, with the following updates:

- please extend the commit message -- feel free to include as much of
  the above discussion as you prefer (assuming you agree with it),

- please include the following snippet in the commit log,  taken before
  and after your patch from the Linux guest dmesg, for *both* i440fx
  *and* q35:

> [    0.247378] ACPI: PCI Interrupt Link [LNKA] (IRQs 5 10 *11)
> [    0.247505] ACPI: PCI Interrupt Link [LNKB] (IRQs 5 10 *11)
> [    0.247629] ACPI: PCI Interrupt Link [LNKC] (IRQs 5 *10 11)
> [    0.247747] ACPI: PCI Interrupt Link [LNKD] (IRQs 5 *10 11)
> [    0.247823] ACPI: PCI Interrupt Link [LNKS] (IRQs *9)
> [    0.292546] PCI Interrupt Link [LNKC] enabled at IRQ 10
> [    0.653097] PCI Interrupt Link [LNKD] enabled at IRQ 11
> [    0.667452] PCI Interrupt Link [LNKA] enabled at IRQ 11
> [    0.682064] PCI Interrupt Link [LNKB] enabled at IRQ 10

  (four snippets in total).

- please also reformat the PciHostIrqs array, near the top of the file,
  in the same patch. Currently it is:

> //
> // Table of host IRQs matching PCI IRQs A-D
> // (for configuring PCI Interrupt Line register)
> //
> CONST UINT8 PciHostIrqs[] = {
>   0x0a, 0x0a, 0x0b, 0x0b
> };

It should go like:

> //
> // Table of (interrupt link) --> (actual interrupt number) mappings; for (a)
> // programming the
> //
> //   (slot, function) --> (interrupt link) --> (actual interrupt number)
> //
> // values into PCI Interrupt Line registers, and for (b) programming the
> //
> //   (interrupt link) --> (actual interrupt number)
> //
> // mappings themselves into the routing (= link configuration) registers.
> /
> CONST UINT8 PciHostIrqs[] = {
>   0x0a, // LNKA, LNKE
>   0x0a, // LNKB, LNKF
>   0x0b, // LNKC, LNKG
>   0x0b  // LNKD, LNKH
> };

Thanks,
Laszlo