Re: [PATCH v4] media: pci: intel: ivsc: improve device reference counting in mei_ace driver

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Ma,

Thanks for the update.

On Tue, Sep 23, 2025 at 11:36:50AM +0800, Ma Ke wrote:
> The device reference counting in mei_ace_setup_dev_link() was
> incomplete, as the reference acquired by device_find_child_by_name()
> was not released immediately on the success path. Add put_device() to

I wouldn't say it's incomplete, that reference is put in the driver's
remove function. The reference may be put right after calling
device_link_add() as device_link_add() takes a reference already. So this
patch would be a cleanup, not a fix.

> properly balance the reference count. Additionally, the redundant
> put_device() in mei_ace_remove() is removed.
> 
> Found by code review.
> 
> Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> ---
> Changes in v4:
> - updated the subject as suggestions;
> Changes in v3:
> - deleted the tag of Fixes and CC, and moved put_device() to immediately after device_link_add() as suggestions;
> Changes in v2:
> - modified the put_device() operations and the patch title as suggestions.
> ---
>  drivers/media/pci/intel/ivsc/mei_ace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/pci/intel/ivsc/mei_ace.c b/drivers/media/pci/intel/ivsc/mei_ace.c
> index 98310b8511b1..9969c02da671 100644
> --- a/drivers/media/pci/intel/ivsc/mei_ace.c
> +++ b/drivers/media/pci/intel/ivsc/mei_ace.c
> @@ -414,6 +414,7 @@ static int mei_ace_setup_dev_link(struct mei_ace *ace)
>  	/* setup link between mei_ace and mei_csi */
>  	ace->csi_link = device_link_add(csi_dev, dev, DL_FLAG_PM_RUNTIME |
>  					DL_FLAG_RPM_ACTIVE | DL_FLAG_STATELESS);
> +	put_device(csi_dev);
>  	if (!ace->csi_link) {
>  		ret = -EINVAL;
>  		dev_err(dev, "failed to link to %s\n", dev_name(csi_dev));

I believe there's still extra put_device() call some lines below from here
on the error path.

> @@ -522,7 +523,6 @@ static void mei_ace_remove(struct mei_cl_device *cldev)
>  	cancel_work_sync(&ace->work);
>  
>  	device_link_del(ace->csi_link);
> -	put_device(ace->csi_dev);
>  
>  	pm_runtime_disable(&cldev->dev);
>  	pm_runtime_set_suspended(&cldev->dev);

-- 
Regards,

Sakari Ailus