[Nouveau] [PATCH v2] pci: Handle 5-bit and 8-bit tag field

[Ilia Mirkin]

On Wed, Sep 16, 2015 at 3:52 PM, Pierre Moreau <pierre.morrow at free.fr> wrote:
> If the hardware supports extended tag field (8-bit ones), then enabled it. This
> is usually done by the VBIOS, but not on some MBPs (see fdo#86537).
> In case extended tag field is not supported, 5-bit tag field is used which
> limits the possible values to 32. Apparently bits 7:0 of 0x8841c stores some
> number of outstanding requests, so cap it to 32 if extended tag is unsupported.
>
> Fixes: fdo#86537
>
> v2: Restrict changes to chipsets >= 0x84
>
> Signed-off-by: Pierre Moreau <pierre.morrow at free.fr>
> ---
>  drm/nouveau/nvkm/subdev/pci/base.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/drm/nouveau/nvkm/subdev/pci/base.c b/drm/nouveau/nvkm/subdev/pci/base.c
> index d1c148e..bbad29d 100644
> --- a/drm/nouveau/nvkm/subdev/pci/base.c
> +++ b/drm/nouveau/nvkm/subdev/pci/base.c
> @@ -46,6 +46,14 @@ nvkm_pci_wr32(struct nvkm_pci *pci, u16 addr, u32 data)
>         pci->func->wr32(pci, addr, data);
>  }
>
> +u32
> +nvkm_pci_mask(struct nvkm_pci *pci, u16 addr, u32 mask, u32 add)

Either add this to the header or make it static. I have a mild
preference for the latter.

> +{
> +       u32 data = pci->func->rd32(pci, addr);
> +       pci->func->wr32(pci, addr, (data & ~mask) | add);
> +       return data;
> +}
> +
>  void
>  nvkm_pci_rom_shadow(struct nvkm_pci *pci, bool shadow)
>  {
> @@ -115,6 +123,23 @@ nvkm_pci_init(struct nvkm_subdev *subdev)
>         if (ret)
>                 return ret;
>
> +       if (pci_is_pcie(pdev) && subdev->device->chipset >= 0x84) {
> +               /* Tag field is 8-bit long, regardless of EXT_TAG.
> +                * However, if EXT_TAG is disabled, only the lower 5 bits of the tag
> +                * field should be used, limiting the number of request to 32.
> +                *
> +                * Apparently, 0x041c stores some limit on the number of requests
> +                * possible, so if EXT_TAG is disabled, limit that requests number to
> +                * 32
> +                *
> +                * Fixes fdo#86537
> +                */
> +               if (nvkm_pci_rd32(pci, 0x007c) & 0x00000020)
> +                       nvkm_pci_mask(pci, 0x0080, 0x00000000, 0x00000100);

Normally this is done as 0x100, 0x100, although your way works.
However a future change might mask out any unwanted bits from the
value as well...

> +               else
> +                       nvkm_pci_mask(pci, 0x041c, 0x00000060, 0x00000000);
> +       }
> +
>         pci->irq = pdev->irq;
>         return ret;
>  }
> --
> 2.5.2
>
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