linux-kernel - [PATCH v2 79/79] media: hantro: document the usage of pm_runtime_get

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Message-Id: <29a5f9cf9680a36fc1f6277364aa7c53776ed0cc.1619518193.git.mchehab+huawei@kernel.org>
Date:   Tue, 27 Apr 2021 12:13:46 +0200
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org
Subject: [PATCH v2 79/79] media: hantro: document the usage of pm_runtime_get_sync()

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@...nel.org>
---
 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;
+
+	/*
+	 * 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;
-- 
2.30.2