linux-kernel - Re: [PATCH] media: i2c: imx274: implement enum_mbus

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Date:   Fri, 19 Nov 2021 10:26:46 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Luca Ceresoli <luca@...aceresoli.net>
Cc:     Eugen Hristev <eugen.hristev@...rochip.com>,
        leonl@...pardimaging.com, linux-media@...r.kernel.org,
        skomatineni@...dia.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: i2c: imx274: implement enum_mbus_code

Hi Luca,

On Thu, Nov 18, 2021 at 06:39:09PM +0100, Luca Ceresoli wrote:
> Hi,
> 
> On 18/11/21 18:26, Sakari Ailus wrote:
> > Hi Luca,
> > 
> > On Thu, Nov 18, 2021 at 06:11:35PM +0100, Luca Ceresoli wrote:
> >> Hi Eugen,
> >>
> >> On 18/11/21 16:40, Eugen Hristev wrote:
> >>> Current driver supports only SRGGB 10 bit RAW bayer format.
> >>> Add the enum_mbus_code implementation to report this format supported.
> >>>
> >>>  # v4l2-ctl -d /dev/v4l-subdev3 --list-subdev-mbus-codes
> >>> ioctl: VIDIOC_SUBDEV_ENUM_MBUS_CODE (pad=0)
> >>>         0x300f: MEDIA_BUS_FMT_SRGGB10_1X10
> >>>  #
> >>>
> >>> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
> >>
> >> Generally OK, but I have a few minor comments.
> >>
> >>> ---
> >>>  drivers/media/i2c/imx274.c | 14 ++++++++++++++
> >>>  1 file changed, 14 insertions(+)
> >>>
> >>> diff --git a/drivers/media/i2c/imx274.c b/drivers/media/i2c/imx274.c
> >>> index 2e804e3b70c4..25a4ef8f6187 100644
> >>> --- a/drivers/media/i2c/imx274.c
> >>> +++ b/drivers/media/i2c/imx274.c
> >>> @@ -1909,7 +1909,21 @@ static int imx274_set_frame_interval(struct stimx274 *priv,
> >>>  	return err;
> >>>  }
> >>>  
> >>> +static int imx274_enum_mbus_code(struct v4l2_subdev *sd,
> >>> +				 struct v4l2_subdev_state *sd_state,
> >>> +				 struct v4l2_subdev_mbus_code_enum *code)
> >>> +{
> >>> +	if (code->index > 0)
> >>> +		return -EINVAL;
> >>
> >> Many driver do check code->pad too, so you might want to do
> >>
> >> 	if (code->pad > 0 || code->index > 0)
> >> 		return -EINVAL;
> > 
> > The caller will have checked the pad exists, and there's a single one on
> > the subdev I suppose.
> 
> Thanks for your explanation. That's very reasonable indeed.
> 
> Now, why do many drivers do that? Old checks that later turned useless
> and nobody ever removed?

Some of those exists, that's for sure. The check was added to the callers a
few years ago I think. Many drivers also have more pads but then they
typically return something else than -EINVAL for the other pads.

-- 
Sakari Ailus