[Intel-gfx] [RFC PATCH] drm/i915: don't treat small BAR as an error with CSS

[Matthew Auld]

On Wed, 11 May 2022 at 11:25, Nirmoy Das <nirmoy.das at intel.com> wrote:
>
> Determine lmem_size using ADDR_RANGE register so that module
> load on platfrom with small bar with css  works.
>
> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
> ---
> I once reserved a dg2 machine with small bar and module load failed on
> it. I can't find that machine anymore hence sending this as RFC.

AFAIK we currently don't want to load the driver on such dg2
configurations, until we first have all the uapi bits landed. The last
patch in that series then turns this on, or at least that's what I
have locally.

>
>  drivers/gpu/drm/i915/gt/intel_region_lmem.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_region_lmem.c b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> index f5111c0a0060..a55eecac104e 100644
> --- a/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> +++ b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> @@ -100,10 +100,19 @@ static struct intel_memory_region *setup_lmem(struct intel_gt *gt)
>         if (!IS_DGFX(i915))
>                 return ERR_PTR(-ENODEV);
>
> +       if (IS_DG1(uncore->i915)) {
> +               lmem_size = pci_resource_len(pdev, 2);

We can drop this, since this is set below also.

> +       } else {
> +               resource_size_t lmem_range;
> +
> +               lmem_range = intel_gt_read_register(&i915->gt0, XEHPSDV_TILE0_ADDR_RANGE) & 0xFFFF;
> +               lmem_size = lmem_range >> XEHPSDV_TILE_LMEM_RANGE_SHIFT;
> +               lmem_size *= SZ_1G;

We can move this under HAS_FLAT_CCS.

I think we need another patch that then just gracefully returns
-EINVAL if this is a small-bar configuration, along with maybe some
helpful drm_err() or so, which can be removed once we properly support
it? Also it looks like we are returning ENODEV in some places here,
which looks iffy.

> +       }
> +
>         if (HAS_FLAT_CCS(i915)) {
>                 u64 tile_stolen, flat_ccs_base;
>
> -               lmem_size = pci_resource_len(pdev, 2);
>                 flat_ccs_base = intel_gt_read_register(gt, XEHPSDV_FLAT_CCS_BASE_ADDR);
>                 flat_ccs_base = (flat_ccs_base >> XEHPSDV_CCS_BASE_SHIFT) * SZ_64K;
>
> --
> 2.35.1
>