linux-kernel - Re: [PATCH v2] drm/vc4: Fix pm_runtime_get

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Message-ID: <96d27d1f-55e4-578a-75e5-686362c05dcf@gmail.com>
Date:   Wed, 20 Apr 2022 16:05:35 +0800
From:   Miaoqian Lin <linmq006@...il.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Emma Anholt <emma@...olt.net>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Eric Anholt <eric@...olt.net>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/vc4: Fix pm_runtime_get_sync() usage


On 2022/4/20 15:51, Maxime Ripard wrote:
> On Wed, Apr 20, 2022 at 12:49:48AM +0000, Miaoqian Lin wrote:
>> If the device is already in a runtime PM enabled state
>> pm_runtime_get_sync() will return 1, so a test for negative
>> value should be used to check for errors.
>>
>> Also, we need to call pm_runtime_put_noidle() when pm_runtime_get_sync()
>> fails, so use pm_runtime_resume_and_get() instead. this function
>> will handle this.
>>
>> Fixes: 4078f5757144 ("drm/vc4: Add DSI driver")
>> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
>> ---
>> change in v2:
>> - switch to pm_runtime_resume_and_get() to fix refcount leak.
>> ---
>>  drivers/gpu/drm/vc4/vc4_dsi.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
>> index 752f921735c6..9d7ffaf6bc70 100644
>> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
>> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
>> @@ -846,8 +846,8 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
>>  	unsigned long phy_clock;
>>  	int ret;
>>  
>> -	ret = pm_runtime_get_sync(dev);
>> -	if (ret) {
>> +	ret = pm_runtime_resume_and_get(dev);
>> +	if (ret < 0) {
> pm_runtime_resume_and_get will return 0 on success, so the previous check was correct

previous check is for pm_runtime_get_sync() not for pm_runtime_resume_and_get (),

I switch to pm_runtime_resume_and_get() to fix the refcount leak bug at the same time.

Sure it's ok to use check if(ret) to check the retval, I just follow a more common way

for usage of pm_runtime_resume_and_get() in the codebase—— check ret<0

Since pm_runtime_resume_and_get() return negative error code.

> Maxime