drm/panthor: Explicitly set the coherency mode

This commit fixes the potential misalignment between the value of device
tree property "dma-coherent" and default value of COHERENCY_ENABLE
register.
Panthor driver didn't explicitly program the COHERENCY_ENABLE register
with the desired coherency mode. The default value of COHERENCY_ENABLE
register is implementation defined, so it may not be always aligned with
the "dma-coherent" property value.
The commit also checks the COHERENCY_FEATURES register to confirm that
the coherency protocol is actually supported or not.

v2:
- Added R-b tags

Signed-off-by: Akash Goel <akash.goel@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20241030225407.4077513-3-akash.goel@arm.com
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
index 2d3529a0b156..0f3cac6ec88e 100644
--- a/drivers/gpu/drm/panthor/panthor_gpu.c
+++ b/drivers/gpu/drm/panthor/panthor_gpu.c
@@ -77,6 +77,12 @@ static const struct panthor_model gpu_models[] = {
 	 GPU_IRQ_RESET_COMPLETED | \
 	 GPU_IRQ_CLEAN_CACHES_COMPLETED)
 
+static void panthor_gpu_coherency_set(struct panthor_device *ptdev)
+{
+	gpu_write(ptdev, GPU_COHERENCY_PROTOCOL,
+		ptdev->coherent ? GPU_COHERENCY_PROT_BIT(ACE_LITE) : GPU_COHERENCY_NONE);
+}
+
 static void panthor_gpu_init_info(struct panthor_device *ptdev)
 {
 	const struct panthor_model *model;
@@ -365,6 +371,9 @@ int panthor_gpu_l2_power_on(struct panthor_device *ptdev)
 			      hweight64(ptdev->gpu_info.shader_present));
 	}
 
+	/* Set the desired coherency mode before the power up of L2 */
+	panthor_gpu_coherency_set(ptdev);
+
 	return panthor_gpu_power_on(ptdev, L2, 1, 20000);
 }