linux-kernel - Re: [PATCH] media: stkwebcam: move stk_camera_read_reg() scratch buffer to struct stk

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Message-ID: <8cab70e2-cd3f-da75-9e6a-1d63e33e6e24@xs4all.nl>
Date:   Wed, 27 Apr 2022 07:38:45 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     trix@...hat.com, mchehab@...nel.org, cai.huoqing@...ux.dev,
        paskripkin@...il.com, xose.vazquez@...il.com
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: stkwebcam: move stk_camera_read_reg() scratch
 buffer to struct stk_camera

Hi Tom,

On 12/03/2022 18:30, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> In stk_camera_read_reg() a single byte buffer is alloc-ed and
> freed on every function call.  Since the size is known,
> move the buffer to the struct stk_camera where it will be alloc-ed
> and freed once.

I read the replies to this patch, but I am not certain if you still want
this patch to be merged, or will make a v2. I have no problem applying this
patch as-is, but I just want to have confirmation that there won't be a v2.

Regards,

	Hans

> 
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  drivers/media/usb/stkwebcam/stk-webcam.c | 11 ++---------
>  drivers/media/usb/stkwebcam/stk-webcam.h |  2 ++
>  2 files changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/media/usb/stkwebcam/stk-webcam.c b/drivers/media/usb/stkwebcam/stk-webcam.c
> index 5b822214ccc5c..787edb3d47c23 100644
> --- a/drivers/media/usb/stkwebcam/stk-webcam.c
> +++ b/drivers/media/usb/stkwebcam/stk-webcam.c
> @@ -150,25 +150,18 @@ int stk_camera_write_reg(struct stk_camera *dev, u16 index, u8 value)
>  int stk_camera_read_reg(struct stk_camera *dev, u16 index, u8 *value)
>  {
>  	struct usb_device *udev = dev->udev;
> -	unsigned char *buf;
>  	int ret;
>  
> -	buf = kmalloc(sizeof(u8), GFP_KERNEL);
> -	if (!buf)
> -		return -ENOMEM;
> -
>  	ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
>  			0x00,
>  			USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
>  			0x00,
>  			index,
> -			buf,
> +			&dev->read_reg_scratch,
>  			sizeof(u8),
>  			500);
>  	if (ret >= 0)
> -		*value = *buf;
> -
> -	kfree(buf);
> +		*value = dev->read_reg_scratch;
>  
>  	if (ret < 0)
>  		return ret;
> diff --git a/drivers/media/usb/stkwebcam/stk-webcam.h b/drivers/media/usb/stkwebcam/stk-webcam.h
> index 14519e5308b18..136decffe9ced 100644
> --- a/drivers/media/usb/stkwebcam/stk-webcam.h
> +++ b/drivers/media/usb/stkwebcam/stk-webcam.h
> @@ -105,6 +105,8 @@ struct stk_camera {
>  	struct list_head sio_avail;
>  	struct list_head sio_full;
>  	unsigned sequence;
> +
> +	u8 read_reg_scratch;
>  };
>  
>  #define vdev_to_camera(d) container_of(d, struct stk_camera, vdev)