linux-kernel - Re: davinci-mcasp: extension to use AHCLKX pin as external clock source

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Message-ID: <54DA12FA.4090402@bytesatwork.ch>
Date:	Tue, 10 Feb 2015 15:17:30 +0100
From:	Urs Fässler <urs.fassler@...esatwork.ch>
To:	Peter Ujfalusi <peter.ujfalusi@...com>, perex@...ex.cz,
	tiwai@...e.de
CC:	lgirdwood@...il.com, broonie@...nel.org, jsarha@...com,
	misael.lopez@...com, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: davinci-mcasp: extension to use AHCLKX pin as external clock
 source

On 06.02.2015 12:50, Peter Ujfalusi wrote:
> On 02/06/2015 11:22 AM, Urs Fässler wrote:
>> The AHCLKX pin seems not to be supported as external source. The first
>> patch is a general fix to allow external clock. The second allows you to
>> select the AHCLKX pin as clock source.
>>
>> Patch built against v3.19-rc7
>>
> 
> I don't think this series is correct. You can just issue:
> snd_soc_dai_set_sysclk(cpu_dai, 0, sysclk, SND_SOC_CLOCK_IN);
> 
> from the machine driver to select AHCLKX as input.
> 
I checked everything and the source of the problem is, that on our
hardware the bit clock of the codec is connected to AHCLKX. According to
the datasheet, AHCLKX is for the master clock only. On the other hand,
it is possible to route a bitclock from AHCLKX to the subsystem (what I
did with my patches).

Now my question is, if it is even worth trying to bring such an option
for the driver (use AHCLKX as bit clock in) upstream?

Thanks
Urs



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