On Fri, Oct 13, 2023 at 03:44:39PM +0200, Nirmoy Das wrote:
> gen8_ggtt_invalidate() is only needed for limited set of platforms
> where GGTT is mapped as WC otherwise this can cause unwanted
> side-effects on XE_HP platforms where GFX_FLSH_CNTL_GEN6 is not
> valid.
>
> v2: Add a func to detect wc ggtt detection (Ville)
>
> Fixes: d2eae8e98d59 ("drm/i915/dg2: Drop force_probe requirement")
> Cc: Rodrigo Vivi <rodrigo.v...@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
> Cc: Jani Nikula <jani.nik...@linux.intel.com>
> Cc: Jonathan Cavitt <jonathan.cav...@intel.com>
> Cc: John Harrison <john.c.harri...@intel.com>
> Cc: Andi Shyti <andi.sh...@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
> Cc: <sta...@vger.kernel.org> # v6.2+
> Suggested-by: Matt Roper <matthew.d.ro...@intel.com>
> Signed-off-by: Nirmoy Das <nirmoy....@intel.com>
> Acked-by: Andi Shyti <andi.sh...@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.ro...@intel.com>
Interestingly, bspec 151 indicates that we probably shouldn't have been
using a CPU:WC mapping for the GGTT on gen9bc platforms either (i.e.,
the GTT part of the GTTMMADR has the same "64-bits or less" restriction
listed as later platforms). But we've been using WC without issue for
the last 8 years, so I guess it's not worth changing it now.
Matt
> ---
> drivers/gpu/drm/i915/gt/intel_ggtt.c | 35 +++++++++++++++++++---------
> 1 file changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> index 4d7d88b92632..401667f83f96 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> @@ -195,6 +195,21 @@ void gen6_ggtt_invalidate(struct i915_ggtt *ggtt)
> spin_unlock_irq(&uncore->lock);
> }
>
> +static bool needs_wc_ggtt_mapping(struct drm_i915_private *i915)
> +{
> + /*
> + * On BXT+/ICL+ writes larger than 64 bit to the GTT pagetable range
> + * will be dropped. For WC mappings in general we have 64 byte burst
> + * writes when the WC buffer is flushed, so we can't use it, but have to
> + * resort to an uncached mapping. The WC issue is easily caught by the
> + * readback check when writing GTT PTE entries.
> + */
> + if (!IS_GEN9_LP(i915) && GRAPHICS_VER(i915) < 11)
> + return true;
> +
> + return false;
> +}
> +
> static void gen8_ggtt_invalidate(struct i915_ggtt *ggtt)
> {
> struct intel_uncore *uncore = ggtt->vm.gt->uncore;
> @@ -202,8 +217,12 @@ static void gen8_ggtt_invalidate(struct i915_ggtt *ggtt)
> /*
> * Note that as an uncached mmio write, this will flush the
> * WCB of the writes into the GGTT before it triggers the invalidate.
> + *
> + * Only perform this when GGTT is mapped as WC, see ggtt_probe_common().
> */
> - intel_uncore_write_fw(uncore, GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);
> + if (needs_wc_ggtt_mapping(ggtt->vm.i915))
> + intel_uncore_write_fw(uncore, GFX_FLSH_CNTL_GEN6,
> + GFX_FLSH_CNTL_EN);
> }
>
> static void guc_ggtt_invalidate(struct i915_ggtt *ggtt)
> @@ -1126,17 +1145,11 @@ static int ggtt_probe_common(struct i915_ggtt *ggtt,
> u64 size)
> GEM_WARN_ON(pci_resource_len(pdev, GEN4_GTTMMADR_BAR) !=
> gen6_gttmmadr_size(i915));
> phys_addr = pci_resource_start(pdev, GEN4_GTTMMADR_BAR) +
> gen6_gttadr_offset(i915);
>
> - /*
> - * On BXT+/ICL+ writes larger than 64 bit to the GTT pagetable range
> - * will be dropped. For WC mappings in general we have 64 byte burst
> - * writes when the WC buffer is flushed, so we can't use it, but have to
> - * resort to an uncached mapping. The WC issue is easily caught by the
> - * readback check when writing GTT PTE entries.
> - */
> - if (IS_GEN9_LP(i915) || GRAPHICS_VER(i915) >= 11)
> - ggtt->gsm = ioremap(phys_addr, size);
> - else
> + if (needs_wc_ggtt_mapping(i915))
> ggtt->gsm = ioremap_wc(phys_addr, size);
> + else
> + ggtt->gsm = ioremap(phys_addr, size);
> +
> if (!ggtt->gsm) {
> drm_err(&i915->drm, "Failed to map the ggtt page table\n");
> return -ENOMEM;
> --
> 2.41.0
>
--
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation
