Re: [Intel-gfx] [PATCH v3] drm/i915: Enable WaProgramMgsrForCorrectSliceSpecificMmioReads for Gen9

Tvrtko Ursulin
2021-03-04T09:12:37Z

On 02/03/2021 06:27, Cooper Chiou wrote:
> WaProgramMgsrForCorrectSliceSpecificMmioReads applies for Gen9 to
> resolve VP8 hardware encoding system hang up on GT1 sku for
> ChromiumOS projects
>
> Slice specific MMIO read inaccurate so MGSR needs to be programmed
> appropriately to get correct reads from these slicet-related MMIOs.
>
> It dictates that before any MMIO read into Slice/Subslice specific
> registers, MCR packet control register(0xFDC) needs to be programmed
> to point to any enabled slice/subslice pair, especially GT1 fused sku
> since this issue can be reproduced on VP8 hardware encoding via ffmpeg
> on ChromiumOS devices.
> When exit PC7, MGSR will reset so that we have to skip fused subslice ID.
>
> Reference: HSD#1508045018,1405586840, BSID#0575
>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: William Tseng <william.tseng@intel.com>
> Cc: Lee Shawn C <shawn.c.lee@intel.com>
>
> Signed-off-by: Cooper Chiou <cooper.chiou@intel.com>
> ---
> drivers/gpu/drm/i915/gt/intel_workarounds.c | 38 +++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> index 3b4a7da60f0b..4ad598a727a6 100644
> --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> @@ -878,9 +878,47 @@ hsw_gt_workarounds_init(struct drm_i915_private *i915, struct i915_wa_list *wal)
> wa_write_clr(wal, GEN7_FF_THREAD_MODE, GEN7_FF_VS_REF_CNT_FFME);
> }
>
> +static void
> +gen9_wa_init_mcr(struct drm_i915_private *i915, struct i915_wa_list *wal)
> +{
> + const struct sseu_dev_info *sseu = &i915->gt.info.sseu;
> + unsigned int slice, subslice;
> + u32 mcr, mcr_mask;
> +
> + GEM_BUG_ON(INTEL_GEN(i915) < 9);
> +
> + /*
> + * WaProgramMgsrForCorrectSliceSpecificMmioReads:glk,kbl,cml
> + * Before any MMIO read into slice/subslice specific registers, MCR
> + * packet control register needs to be programmed to point to any
> + * enabled s/ss pair. Otherwise, incorrect values will be returned.
> + * This means each subsequent MMIO read will be forwarded to an
> + * specific s/ss combination, but this is OK since these registers
> + * are consistent across s/ss in almost all cases. In the rare
> + * occasions, such as INSTDONE, where this value is dependent
> + * on s/ss combo, the read should be done with read_subslice_reg.
> + */
> + slice = fls(sseu->slice_mask) - 1;
> + GEM_BUG_ON(slice >= ARRAY_SIZE(sseu->subslice_mask));
> + subslice = fls(intel_sseu_get_subslices(sseu, slice));
> + GEM_BUG_ON(!subslice);
> + subslice--;
> +
> + mcr = GEN8_MCR_SLICE(slice) | GEN8_MCR_SUBSLICE(subslice);
> + mcr_mask = GEN8_MCR_SLICE_MASK | GEN8_MCR_SUBSLICE_MASK;
> +
> + drm_dbg(&i915->drm, "MCR slice:%d/subslice:%d = %x\n", slice, subslice, mcr);
> +
> + wa_write_clr_set(wal, GEN8_MCR_SELECTOR, mcr_mask, mcr);
> +}

Have you considered reusing existing wa_init_mcr? Just needs the
top-level assert changed and otherwise it looks it would do the right
thing for Gen9. Advantage being a smaller patch and less code to carry.

Regards,

Tvrtko

> +
> static void
> gen9_gt_workarounds_init(struct drm_i915_private *i915, struct i915_wa_list *wal)
> {
> + /* WaProgramMgsrForCorrectSliceSpecificMmioReads:glk,kbl,cml */
> + if (!IS_COFFEELAKE(i915))
> + gen9_wa_init_mcr(i915, wal);
> +
> /* WaDisableKillLogic:bxt,skl,kbl */
> if (!IS_COFFEELAKE(i915) && !IS_COMETLAKE(i915))
> wa_write_or(wal,
>