Re: [PATCH 2/2] drm/panfrost: Use coherent pagetable walk on Juno

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On 30/09/2019 17:26, Steven Price wrote:
On 30/09/2019 16:24, Robin Murphy wrote:
Although going full "dma-coherent" ends badly due to GEM objects still
being forcibly mapped non-cacheable, we can at least take advantage of
Juno's ACE-lite integration to skip cache maintenance for pagetables.

CC: Rob Herring <robh@xxxxxxxxxx>
CC: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
---

This isn't really meant as a series, I'm just sending it together
with patch #1 for context.

  drivers/gpu/drm/panfrost/panfrost_mmu.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index bdd990568476..560439f63277 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -365,6 +365,9 @@ int panfrost_mmu_pgtable_alloc(struct panfrost_file_priv *priv)
  		.iommu_dev	= pfdev->dev,
  	};
+ if (of_device_is_compatible(pfdev->dev->of_node, "arm,juno-mali"))
+		pfdev->mmu->pgtbl_cfg.coherent_walk = true;

Should be:
	mmu->pgtbl_cfg.coherent_walk = true;

Oops, yes, rebase error.

Also I'm not sure whether we should do this based on a compatible
string. kbase has a "system-coherency" device-tree flag for it. In
theory we could end up with a long list of compatibles here...

Right, ideally we'd just infer everything we need from "dma-coherent", but to be able to set that without causing fireworks we need the GEM mmap implementation to be able to play along too. Maybe this can wait until I figure out how to address that at the same time...

And either way, it would probably be better to detect anything SoC-specific once at probe and stash it in a feature flag - TBH this patch is more of a proof-of-concept than anything.

Thanks,
Robin.


Steve

+
  	mmu->pgtbl_ops = alloc_io_pgtable_ops(ARM_MALI_LPAE, &mmu->pgtbl_cfg,
  					      priv);
  	if (!mmu->pgtbl_ops)


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