Re: [PATCH v3 79/79] media: hantro: document the usage of pm_runtime_get_sync()

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On 2021-04-27 11:27, Mauro Carvalho Chehab wrote:
Despite other *_get()/*_put() functions, where usage count is
incremented only if not errors, the pm_runtime_get_sync() has
a different behavior, incrementing the counter *even* on
errors.

That's an error prone behavior, as people often forget to
decrement the usage counter.

However, the hantro driver depends on this behavior, as it
will decrement the usage_count unconditionally at the m2m
job finish time, which makes sense.

So, intead of using the pm_runtime_resume_and_get() that
would decrement the counter on error, keep the current
API, but add a documentation explaining the rationale for
keep using pm_runtime_get_sync().

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
---
  drivers/staging/media/hantro/hantro_drv.c | 7 +++++++
  1 file changed, 7 insertions(+)

diff --git a/drivers/staging/media/hantro/hantro_drv.c b/drivers/staging/media/hantro/hantro_drv.c
index 595e82a82728..96f940c1c85c 100644
--- a/drivers/staging/media/hantro/hantro_drv.c
+++ b/drivers/staging/media/hantro/hantro_drv.c
@@ -155,6 +155,13 @@ static void device_run(void *priv)
  	ret = clk_bulk_enable(ctx->dev->variant->num_clocks, ctx->dev->clocks);
  	if (ret)
  		goto err_cancel_job;

..except this can also cause the same pm_runtime_put_autosuspend() call without even reaching the "matching" get below, so rather than some kind of cleverness it seems more like it's just broken :/

Robin.

+
+	/*
+	 * The pm_runtime_get_sync() will increment dev->power.usage_count,
+	 * even on errors. That's the expected behavior here, since the
+	 * hantro_job_finish() function at the error handling code
+	 * will internally call pm_runtime_put_autosuspend().
+	 */
  	ret = pm_runtime_get_sync(ctx->dev->dev);
  	if (ret < 0)
  		goto err_cancel_job;

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