drm/panfrost: Perform hard reset to recover GPU if soft reset fails

Even though soft reset should ideally never fail, during development of
some power management features I managed to get some bits wrong: this
resulted in GPU soft reset failures, where the GPU was never able to
recover, not even after suspend/resume cycles, meaning that the only
way to get functionality back was to reboot the machine.

Perform a hard reset after a soft reset failure to be able to recover
the GPU during runtime (so, without any machine reboot).
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231109102543.42971-2-angelogioacchino.delregno@collabora.com

drivers/gpu/drm/panfrost/panfrost_gpu.c

@@ -60,14 +60,21 @@ int panfrost_gpu_soft_reset(struct panfrost_device *pfdev)
 
 	gpu_write(pfdev, GPU_INT_MASK, 0);
 	gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_RESET_COMPLETED);
-	gpu_write(pfdev, GPU_CMD, GPU_CMD_SOFT_RESET);
 
+	gpu_write(pfdev, GPU_CMD, GPU_CMD_SOFT_RESET);
 	ret = readl_relaxed_poll_timeout(pfdev->iomem + GPU_INT_RAWSTAT,
 		val, val & GPU_IRQ_RESET_COMPLETED, 100, 10000);
 
 	if (ret) {
-		dev_err(pfdev->dev, "gpu soft reset timed out\n");
-		return ret;
+		dev_err(pfdev->dev, "gpu soft reset timed out, attempting hard reset\n");
+
+		gpu_write(pfdev, GPU_CMD, GPU_CMD_HARD_RESET);
+		ret = readl_relaxed_poll_timeout(pfdev->iomem + GPU_INT_RAWSTAT, val,
+						 val & GPU_IRQ_RESET_COMPLETED, 100, 10000);
+		if (ret) {
+			dev_err(pfdev->dev, "gpu hard reset timed out\n");
+			return ret;
+		}
 	}
 
 	gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_MASK_ALL);

drivers/gpu/drm/panfrost/panfrost_regs.h

@@ -44,6 +44,7 @@
 	 GPU_IRQ_MULTIPLE_FAULT)
 #define GPU_CMD				0x30
 #define   GPU_CMD_SOFT_RESET		0x01
+#define   GPU_CMD_HARD_RESET		0x02
 #define   GPU_CMD_PERFCNT_CLEAR		0x03
 #define   GPU_CMD_PERFCNT_SAMPLE	0x04
 #define   GPU_CMD_CYCLE_COUNT_START	0x05