linux-kernel - Re: [PATCH] media: coda: Fix runtime PM imbalance in coda

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Message-ID: <20200525123838.GA12983@pengutronix.de>
Date:   Mon, 25 May 2020 14:38:38 +0200
From:   Philipp Zabel <pza@...gutronix.de>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     kjlu@....edu, Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: coda: Fix runtime PM imbalance in coda_probe

Hi Dinghao,

thank you for the patch! The first part is fine, but I think the second
part is not necessary, see below:

On Sat, May 23, 2020 at 06:03:32PM +0800, Dinghao Liu wrote:
> When coda_firmware_request() returns an error code,
> a pairing runtime PM usage counter decrement is needed
> to keep the counter balanced.
> 
> Also, the caller expects coda_probe() to increase PM
> usage counter, there should be a refcount decrement
> in coda_remove() to keep the counter balanced.

coda_probe() increments the usage counter only until coda_fw_callback()
decrements it again. Where is the imbalance?

> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  drivers/media/platform/coda/coda-common.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/platform/coda/coda-common.c b/drivers/media/platform/coda/coda-common.c
> index d0d093dd8f7c..550e9a1266da 100644
> --- a/drivers/media/platform/coda/coda-common.c
> +++ b/drivers/media/platform/coda/coda-common.c
> @@ -3119,6 +3119,8 @@ static int coda_probe(struct platform_device *pdev)
>  	return 0;
>  
>  err_alloc_workqueue:
> +	pm_runtime_disable(&pdev->dev);
> +	pm_runtime_put_noidle(&pdev->dev);

These seem right, they balance out the pm_runtime_enable()
and pm_runtime_get_noresume() right before the error.

>  	destroy_workqueue(dev->workqueue);
>  err_v4l2_register:
>  	v4l2_device_unregister(&dev->v4l2_dev);
> @@ -3136,6 +3138,7 @@ static int coda_remove(struct platform_device *pdev)
>  	}
>  	if (dev->m2m_dev)
>  		v4l2_m2m_release(dev->m2m_dev);
> +	pm_runtime_put_noidle(&pdev->dev);

I think this is incorrect. There is one pm_runtime_get_noresume() in
coda_probe(), and one pm_runtime_put_sync() in coda_fw_callback().
By the time coda_remove() is called, balance is already restored.

regards
Philipp