[devel] [PATCH 19/35] drm/panfrost: forcibly set dma-coherent on Baikal-M

[asheplyakov на yandex.ru]

From: Alexey Sheplyakov <asheplyakov на altlinux.org>

With memattr 0x888d88 (set by arm_mali_lpae_alloc_pgtable) GPU
(Mali T628 r1p0) experiences a lot of DATA_INVALID faults,
unhandled page faults, and other errors. Also the screen goes
black almost immediately.

On the other hand with memattr 0x484d48 (as set by mali_kbase)
the GPU appears to work just fine.

Robin Murphy <robin.murphy на arm.com> explains:

> using the outer-cacheable attribute is deliberate because it is necessary
> for I/O-coherent GPUs to work properly (and should be irrelevant for
> non-coherent integrations)

> I'd note that panfrost has been working OK - to the extent that Mesa
> supports its older ISA - on the T624 (single core group) in Arm's
> Juno SoC for over a year now since commit 268af50f38b1.

> If you have to force outer non-cacheable to avoid getting translation
> faults and other errors that look like the GPU is inexplicably seeing
> the wrong data, I'd check whether you have the same thing where your
> integration is actually I/O-coherent and you're missing the "dma-coherent"
> property in your DT.

Indeed setting the "gpu-coherent" property (and adjusting jobs affinity
for dual core group GPU) makes panfrost work just fine on Baikal-M.

However on Baikal-M the FDT is passed to the kernel by the firmware,
and replacing the FDT in the firmware is tricky.
Therefore set `coherent` property when running on Baikal-M (even
if the `dma-coherent` property is missing in the FDT).

X-DONTUPSTREAM
X-feature-Baikal-M
---
 drivers/gpu/drm/panfrost/panfrost_drv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index 96bb5a465627..8752bffbac98 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -561,6 +561,10 @@ static int panfrost_probe(struct platform_device *pdev)
 		return -ENODEV;
 
 	pfdev->coherent = device_get_dma_attr(&pdev->dev) == DEV_DMA_COHERENT;
+	if (!pfdev->coherent && of_device_is_compatible(of_root, "baikal,baikal-m")) {
+		pfdev->coherent = true;
+		dev_warn(&pdev->dev, "marking as DMA coherent on BE-M1000");
+	}
 
 	/* Allocate and initialze the DRM device. */
 	ddev = drm_dev_alloc(&panfrost_drm_driver, &pdev->dev);
-- 
2.32.0