[PATCH v4] drm/panfrost: Sync IRQ by job's timeout handler

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

Panfrost IRQ handler may stuck for a long time, for example this happens
when there is a bad HDMI connection and HDMI handler takes a long time to
finish processing, holding Panfrost. Make Panfrost's job timeout handler
to sync IRQ before checking fence signal status in order to prevent
spurious job timeouts due to a slow IRQ processing.

Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> # MediaTek MT8192 and MT8195 Chromebooks
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---

Changelog:

v4: - Improved comment like was suggested by Boris and added his r-b.

v3: - Added comment to the code as was suggested by Boris

    - Added r-b/t-b from Steven and Angelo

v2: - Moved synchronize_irq() after first signal-check to avoid unnecessary
      blocking on syncing.

    - Added warn message about high interrupt latency.

 drivers/gpu/drm/panfrost/panfrost_job.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index dbc597ab46fb..db6d9a17004f 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -720,6 +720,22 @@ static enum drm_gpu_sched_stat panfrost_job_timedout(struct drm_sched_job
 	if (dma_fence_is_signaled(job->done_fence))
 		return DRM_GPU_SCHED_STAT_NOMINAL;
 
+	/*
+	 * Panfrost IRQ handler may take a long time to process an interrupt
+	 * if there is another IRQ handler hogging the processing.
+	 * For example, the HDMI encoder driver might be stuck in the IRQ
+	 * handler for a significant time in a case of bad cable connection.
+	 * In order to catch such cases and not report spurious Panfrost
+	 * job timeouts, synchronize the IRQ handler and re-check the fence
+	 * status.
+	 */
+	synchronize_irq(pfdev->js->irq);
+
+	if (dma_fence_is_signaled(job->done_fence)) {
+		dev_warn(pfdev->dev, "unexpectedly high interrupt latency\n");
+		return DRM_GPU_SCHED_STAT_NOMINAL;
+	}
+
 	dev_err(pfdev->dev, "gpu sched timeout, js=%d, config=0x%x, status=0x%x, head=0x%x, tail=0x%x, sched_job=%p",
 		js,
 		job_read(pfdev, JS_CONFIG(js)),
-- 
2.41.0