linux-kernel - [PATCH v0 4/9] media: qcom: camss: Fix VFE-17x vfe_disable

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Message-ID: <20230814141007.3721197-5-bryan.odonoghue@linaro.org>
Date:   Mon, 14 Aug 2023 15:10:02 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     rfoss@...nel.org, todor.too@...il.com, bryan.odonoghue@...aro.org,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        mchehab@...nel.org, hverkuil-cisco@...all.nl,
        sakari.ailus@...ux.intel.com, andrey.konovalov@...aro.org
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH v0 4/9] media: qcom: camss: Fix VFE-17x vfe_disable_output()

There are two problems with the current vfe_disable_output() routine.

Firstly we rightly use a spinlock to protect output->gen2.active_num
everywhere except for in the IDLE timeout path of vfe_disable_output().
Even if that is not racy "in practice" somehow it is by happenstance not
by design.

Secondly we do not get consistent behaviour from this routine. On
sc8280xp 50% of the time I get "VFE idle timeout - resetting". In this
case the subsequent capture will succeed. The other 50% of the time, we
don't hit the idle timeout, never do the VFE reset and subsequent
captures stall indefinitely.

Rewrite the vfe_disable_output() routine to

- Quiesce write masters with vfe_wm_stop()
- Set active_num = 0

remembering to hold the spinlock when we do so followed by

- Reset the VFE

Testing on sc8280xp and sdm845 shows this to be a valid fix.

Fixes: 7319cdf189bb ("media: camss: Add support for VFE hardware version Titan 170")
Cc: stable@...r.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
---
 .../media/platform/qcom/camss/camss-vfe-170.c | 19 +++----------------
 1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/drivers/media/platform/qcom/camss/camss-vfe-170.c b/drivers/media/platform/qcom/camss/camss-vfe-170.c
index 02494c89da91c..ae9137633c301 100644
--- a/drivers/media/platform/qcom/camss/camss-vfe-170.c
+++ b/drivers/media/platform/qcom/camss/camss-vfe-170.c
@@ -500,28 +500,15 @@ static int vfe_disable_output(struct vfe_line *line)
 	struct vfe_output *output = &line->output;
 	unsigned long flags;
 	unsigned int i;
-	bool done;
-	int timeout = 0;
-
-	do {
-		spin_lock_irqsave(&vfe->output_lock, flags);
-		done = !output->gen2.active_num;
-		spin_unlock_irqrestore(&vfe->output_lock, flags);
-		usleep_range(10000, 20000);
-
-		if (timeout++ == 100) {
-			dev_err(vfe->camss->dev, "VFE idle timeout - resetting\n");
-			vfe_reset(vfe);
-			output->gen2.active_num = 0;
-			return 0;
-		}
-	} while (!done);
 
 	spin_lock_irqsave(&vfe->output_lock, flags);
 	for (i = 0; i < output->wm_num; i++)
 		vfe_wm_stop(vfe, output->wm_idx[i]);
+	output->gen2.active_num = 0;
 	spin_unlock_irqrestore(&vfe->output_lock, flags);
 
+	vfe_reset(vfe);
+
 	return 0;
 }
 
-- 
2.41.0