linux-kernel - Re: [PATCH v6 2/3] media: i2c: adv748x: add adv748x driver

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Date:   Mon, 3 Jul 2017 16:00:46 +0100
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     kieran.bingham@...asonboard.com, Hans Verkuil <hverkuil@...all.nl>,
        linux-renesas-soc@...r.kernel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     laurent.pinchart@...asonboard.com, niklas.soderlund@...natech.se,
        hans.verkuil@...co.com, Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Steve Longerbeam <slongerbeam@...il.com>,
        Pavel Machek <pavel@....cz>,
        Ramesh Shanmugasundaram <ramesh.shanmugasundaram@...renesas.com>,
        Todor Tomov <todor.tomov@...aro.org>,
        Hyungwoo Yang <hyungwoo.yang@...el.com>
Subject: Re: [PATCH v6 2/3] media: i2c: adv748x: add adv748x driver

Hi Hans,

On 03/07/17 15:45, Kieran Bingham wrote:
> Hi Hans,
> 
> Thanks for your review,
> 
> On 03/07/17 14:51, Hans Verkuil wrote:
>> On 06/27/2017 05:03 PM, Kieran Bingham wrote:
>>> From: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
>>>
>>> Provide support for the ADV7481 and ADV7482.

...

>>> +/* -----------------------------------------------------------------------------
>>> + * HDMI and CP
>>> + */
>>> +
>>> +#define ADV748X_HDMI_MIN_WIDTH        640
>>> +#define ADV748X_HDMI_MAX_WIDTH        1920
>>> +#define ADV748X_HDMI_MIN_HEIGHT        480
>>> +#define ADV748X_HDMI_MAX_HEIGHT        1200
>>> +#define ADV748X_HDMI_MIN_PIXELCLOCK    0        /* unknown */
>>
>> 0 makes no sense. Something like 13000000 would work better (pixelclock rate for
>> V4L2_DV_BT_CEA_720X480I59_94 is 13500000).
> 
> This is another one that must have got lost somehow - you'd already told me this
> and I'm really sure I changed it to the value you suggested ...
> 
> /me is confused at code loss - Must have been a rebase gone bad. :-(
> 
> 
>>> +#define ADV748X_HDMI_MAX_PIXELCLOCK    162000000
>>
>> You probably based that on the 1600x1200p60 format?
> 
> No idea I'm afraid - it's the value that was set when I recieved the driver...
> 
>>
>> 162MHz is a bit low for an adv receiver. The adv7604 and adv8742 have a max rate
>> of 225 MHz.
>> This should be documented in the datasheet.
> 
> Hrm ... haven't found it yet - I'll keep digging....


I've found this as the most relevant reference:

================================================================================
The ADV7481 HDMI capable receiver supports a maximum pixel clock frequency of
162 MHz, allowing HDTV formats up to 1080p, and display resolutions up to UXGA
(1600 × 1200 at 60 Hz). The device integrates a consumer electronics control
(CEC) controller that supports the capability discovery and control (CDC)
feature. The HDMI input port has dedicated 5 V detect and Hot PlugTM assert pins.
================================================================================

So that certainly looks like 162 MHz is the correct value.

>> Besides, you need a bit of margin since detected pixelclock rates can be a bit off.

Does that mean you would you recommend adding 0.5 MHz to the 162 MHz in a
similar way as the minimum, or keep at 162 MHz ?

(I'm assuming stay at 162 MHz, as the 7604 is set at 225MHz)

--
Regards

Kieran