Re: [PATCH 3/5] drm/panfrost: add support for reset quirk

From: Steven Price
Date: Wed Sep 09 2020 - 08:32:39 EST

On 08/09/2020 16:18, Neil Armstrong wrote:
The T820, G31 & G52 GPUs integratewd by Amlogic in the respective GXM, G12A/SM1 & G12B
SoCs needs a quirk in the PWR registers at the GPU reset time.

This adds a callback in the device compatible struct of permit this.

Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
drivers/gpu/drm/panfrost/panfrost_device.h | 3 +++
drivers/gpu/drm/panfrost/panfrost_gpu.c | 4 ++++
2 files changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
index 2cf1a6a13af8..4c9cd5452ba5 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -73,6 +73,9 @@ struct panfrost_compatible {
/* IOMMU quirks flags */
unsigned long pgtbl_quirks;
+ /* Vendor implementation quirks at reset time callback */
+ void (*vendor_reset_quirk)(struct panfrost_device *pfdev);
struct panfrost_device {
diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
index e0f190e43813..c129aaf77790 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
@@ -62,6 +62,10 @@ int panfrost_gpu_soft_reset(struct panfrost_device *pfdev)
gpu_write(pfdev, GPU_CMD, GPU_CMD_SOFT_RESET);
+ /* The Amlogic GPU integration needs quirks at this stage */
+ if (pfdev->comp->vendor_reset_quirk)
+ pfdev->comp->vendor_reset_quirk(pfdev);
ret = readl_relaxed_poll_timeout(pfdev->iomem + GPU_INT_RAWSTAT,
val, val & GPU_IRQ_RESET_COMPLETED, 100, 10000);

Placing the quirk before the reset has completed is dodgy. Can this be ordered after the GPU_IRQ_RESET_COMPLETED signal has been seen? The problem is the reset could (in theory) cause a power transition (e.g. if the GPU is reset while a core is powered) and changing the PWR_OVERRIDEx registers during a transition is undefined. But I don't know the details of how the hardware is broken so it is possible the override is needed for the reset to complete so this would need testing.

I also wonder if this could live in panfrost_gpu_init_quirks() instead? Although that is mostly about quirks common to all Mali GPU implementations rather than a specific implementation. Although now I've looked I've noticed we have a bug as we don't appear to reapply those quirks after a reset - I'll send a patch!