From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Nelson <eric.nelson@boundarydevices.com>
Subject: Re: [PATCH V2] ASoC: sgtl5000: add delay before first
 I2C access
Date: Fri, 30 Jan 2015 15:02:02 -0700
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To: Nikolay Dimitrov <picmaster@mail.bg>
Cc: Takashi Iwai <tiwai@suse.de>, Fabio Estevam <fabio.estevam@freescale.com>, "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>, Mark Brown <broonie@kernel.org>, Fabio Estevam <festevam@gmail.com>
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Hi Nikolay,

On 01/30/2015 02:50 PM, Nikolay Dimitrov wrote:
> Hi Eric,
> 
> On 01/30/2015 11:31 PM, Fabio Estevam wrote:
>> Hi Eric,
>>
>> On Fri, Jan 30, 2015 at 7:07 PM, Eric Nelson
>> <eric.nelson@boundarydevices.com> wrote:
>>> To quote from section 1.3.1 of the data sheet:
>>>          The SGTL5000 has an internal reset that is deasserted
>>>          8 SYS_MCLK cycles after all power rails have been brought
>>>          up. After this time, communication can start
>>>
>>>          ...
>>>          1.0uS represents 8 SYS_MCLK cycles at the minimum 8.0 MHz
>>> SYS_MCLK.
>>
>> Small detail: Should be us instead of uS.
> 
> FYI - If you're observing issues with communicating with SGTL5000 I2C,
> please make sure also that the chip has a valid clock signal on
> SYS_MCLK, otherwise it won't respond on I2C transactions (I2C will work
> with any SYS_MCLK in the range 8-27MHz).
> 

Thanks for that, but the issue we're seeing and that made me spot this
was a very intermittent problem (1 in many 1000's of boots) reported by
a customer on our 3.10.17 code base.

We haven't been able to repeat the issue, but the failure is in the
initial read of the CHIP_ID register (i.e. the first I2C access) and
the docs clearly state that a 1us delay is needed.

I haven't found the commit that removed it, but earlier versions
of sgtl5000.c had a udelay(10) before the first I2C access.

Regards,


Eric