linux-kernel - Re: [PATCH v9 2/4] media: i2c: Add MAX9286 driver

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Message-ID: <20200526085450.GF8214@valkosipuli.retiisi.org.uk>
Date:   Tue, 26 May 2020 11:54:50 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        linux-renesas-soc@...r.kernel.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Niklas Söderlund 
        <niklas.soderlund@...natech.se>, Hans Verkuil <hverkuil@...all.nl>,
        Hyun Kwon <hyunk@...inx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>
Subject: Re: [PATCH v9 2/4] media: i2c: Add MAX9286 driver

Hi Laurent,

On Wed, May 20, 2020 at 03:50:20AM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Mon, May 18, 2020 at 12:45:18PM +0100, Kieran Bingham wrote:
> > Hi Sakari,
> > 
> > There are only fairly minor comments here, fix ups will be included in a
> > v10.
> > 
> > Is there anything major blocking integration?
> > 
> > On 16/05/2020 22:51, Sakari Ailus wrote:
> > > On Tue, May 12, 2020 at 04:51:03PM +0100, Kieran Bingham wrote:
> > > 
> > > ...
> > > 
> > >> +static int max9286_enum_mbus_code(struct v4l2_subdev *sd,
> > >> +				  struct v4l2_subdev_pad_config *cfg,
> > >> +				  struct v4l2_subdev_mbus_code_enum *code)
> > >> +{
> > >> +	if (code->pad || code->index > 0)
> > >> +		return -EINVAL;
> > >> +
> > >> +	code->code = MEDIA_BUS_FMT_UYVY8_2X8;
> > > 
> > > Why UYVY8_2X8 and not UYVY8_1X16? In general, the single sample / pixel
> > > variant of the format is generally used on the serial busses. This choice
> > > was made when serial busses were introduced.
> 
> This is a bit of a tricky one. On the camera size, for the RDACM20, the
> O10635 sensor outputs UYVY8_2X8. This if fed to the MAX9271 serializer,
> which doesn't care about the data type. The MAX9271 has a 16-bit input
> bus, with 10 bits reserved for data, 2 bits dynamically configurable
> to carry H/V sync or extra data, and 4 bits dynamically configurable to
> carry GPIOs or extra data. The 16-bit words are then serialized (it's a
> bit more complicated, when using the H/V sync signals they are
> transmitted in a different way, and the MAX9271 also supports a DDR mode
> that makes the "serial link word" carry up to 30 bits). Effectively, the
> two samples of UYVY8_2X8 are serialized in a 16-bit word each.
> 
> Sakari, with this information in mind, what would you recommend ?

As this pad describes a serial bus --- doesn't it? --- it should use the
same formats as other serial busses such as CSI-2. I.e. the 1X16 variant.

-- 
Regards,

Sakari Ailus