linux-kernel - Re: [PATCH v4] media: i2c: add support for omnivision's ov2659 sensor

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Date:	Wed, 11 Mar 2015 19:40:13 +0000
From:	"Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Sakari Ailus <sakari.ailus@....fi>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	LMML <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v4] media: i2c: add support for omnivision's ov2659 sensor

Hi Laurent,

Thanks for the review.

On Wed, Mar 11, 2015 at 6:22 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Tuesday 10 March 2015 03:35:57 Sakari Ailus wrote:
>> On Sun, Mar 08, 2015 at 11:33:27AM +0000, Lad Prabhakar wrote:
>> ...
>>
>> > +static struct ov2659_platform_data *
>> > +ov2659_get_pdata(struct i2c_client *client)
>> > +{
>> > +   struct ov2659_platform_data *pdata;
>> > +   struct device_node *endpoint;
>> > +   int ret;
>> > +
>> > +   if (!IS_ENABLED(CONFIG_OF) || !client->dev.of_node) {
>> > +           dev_err(&client->dev, "ov2659_get_pdata: DT Node found\n");
>> > +           return client->dev.platform_data;
>> > +   }
>> > +
>> > +   endpoint = of_graph_get_next_endpoint(client->dev.of_node, NULL);
>> > +   if (!endpoint)
>> > +           return NULL;
>> > +
>> > +   pdata = devm_kzalloc(&client->dev, sizeof(*pdata), GFP_KERNEL);
>> > +   if (!pdata)
>> > +           goto done;
>> > +
>> > +   ret = of_property_read_u32(endpoint, "link-frequencies",
>> > +                              &pdata->link_frequency);
>>
>> This is actually documented as being a 64-bit array.
>
> The main purpose of link-frequencies is to restrict the link frequencies
> acceptable in the system due to EMI requirements. One link frequency should be
> selected in the array based on the desired format and frame rate. This is
> usually done by exposing the frequency to userspace through a writable
> V4L2_CID_LINK_FREQ control, and exposing the resulting pixel rate as a read-
> only V4L2_CID_PIXEL_RATE control.
>
> V4L2_CID_PIXEL_RATE is mandatory to use the sensor with several drivers
> (including omap3isp and omap4iss), so it should really be implemented.
>
Even if the sensor supports only one frequency the control needs to be
implemented ?

Cheers,
--Prabhakar Lad
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