linux-kernel - Re: [PATCH] ARM: davinci: dm644x: fix out range signal for ED

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Date:	Fri, 26 Oct 2012 13:14:33 +0530
From:	Prabhakar Lad <prabhakar.csengg@...il.com>
To:	Sekhar Nori <nsekhar@...com>
Cc:	DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
	Manjunath Hadli <manjunath.hadli@...com>,
	VGER <linux-kernel@...r.kernel.org>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	"Lad, Prabhakar" <prabhakar.lad@...com>
Subject: Re: [PATCH] ARM: davinci: dm644x: fix out range signal for ED

Sekhar,

On Fri, Oct 26, 2012 at 1:05 PM, Sekhar Nori <nsekhar@...com> wrote:
> On 10/4/2012 7:23 PM, Prabhakar Lad wrote:
>> Sekhar
>>
>> On Thu, Oct 4, 2012 at 12:43 PM, Sekhar Nori <nsekhar@...com> wrote:
>>> On 10/4/2012 10:22 AM, Prabhakar Lad wrote:
>>>> Hi Sekhar,
>>>>
>>>> On Wed, Oct 3, 2012 at 4:08 PM, Sekhar Nori <nsekhar@...com> wrote:
>>>>> On 10/3/2012 12:05 PM, Prabhakar wrote:
>>>>>> From: Lad, Prabhakar <prabhakar.lad@...com>
>>>>>>
>>>>>> while testing display on dm644x, for ED out-range signals
>>>>>> was observed. This patch fixes appropriate clock setting
>>>>>> for ED.
>>>>>
>>>>> Can you please clarify what you mean by "out range signal"? Are there
>>>>> any user visible artifacts on the display? What was the clock being
>>>>> provided earlier and what is the value after this patch?
>>>>>
>>>>> Also, is the issue severe enough that this patch should be applied to
>>>>> stable tree as well?
>>>>>
>>>> Ideally a clock of 54Mhz is required for  enhanced definition to
>>>> work, which it was actually set to but while testing I noticed
>>>> out-of-range signal. The out-of-range signal is often caused
>>>> when the field rate is above the rate that the television will handle.
>>>> When this is the case the TV or monitor displays "Out-Of-Range Signal".
>>>>
>>>> Reducing the clock fixed it. now the clock is set to 27Mhz.
>>>
>>> So, is the requirement for ED 54MHz or lower? Still trying to explain
>>> myself how 27MHz is working where a 54MHz is required. I guess there is
>>> also a lower limit on what the frequency should be?
>>>
>> Ideally its 54Mhz, but I see in the datasheet for AD7342/3 [1] it can also
>> work at 27Mhz too.
>
> So, based on this discussion I think a better description would be:
>
> "
> Fix the video clock setting when custom timings are used with pclock  <=
> 27MHz. Existing clock selection uses PLL2 mode which results in a 54MHz
> clock where as using the MXI mode results in a 27MHz clock (which is the
> one actually desired).
>
> This affects the Enhanced Definition (ED) support on DM644x. Without
> this patch, out-range signals errors are were observed on the TV. An
> out-of-range signal is often caused when the field rate is above the
> rate that the television will handle.
> "
>
> Is this accurate? In future, please try to be descriptive in patch
> description as it will help understand what the patch is doing and why
> (which in turn will lead to the patch getting accepted faster).
>
Looks good.  I'll make sure to have descriptive commit message hence forth.

> Also I assume you need this patch in v3.7? Or can I send it for v3.8?
>
Since its a fix it would be good if its queued for v3.7.

Regards,
--Prabhakar

> Thanks,
> Sekhar
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