linux-kernel - Re: Using regmap_update_bits to update a write only register

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Message-ID: <54F9A171.5000107@metafoo.de>
Date:	Fri, 06 Mar 2015 13:45:37 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Mark Brown <broonie@...nel.org>,
	Daniel Baluta <daniel.baluta@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Using regmap_update_bits to update a write only register

On 03/06/2015 12:21 PM, Mark Brown wrote:
> On Thu, Mar 05, 2015 at 08:14:14PM +0200, Daniel Baluta wrote:
>> On Mar 5, 2015 7:54 PM, "Mark Brown" <broonie@...nel.org> wrote:
>
>>> Probably, or there's a bug.  What should happen is that if the register
>>> default appeared successfully then the read will get statisfied from the
>>> cache in the manner you describe - presumably that's gone wrong somehow.
>>> Have you set num_reg_defaults?  That's the obvious thing...
>
>> Did that. I will have a closer look. Thanks for the answer.
>
> OK, the other thing that springs to mind to check is that the register
> didn't somehow get marked as volatile.
>

There were some bugs in the past were non-readable register automatically 
got marked as volatile, this has been fixed though a few months ago. Try to 
make sure you use the latest upstream version of regmap.

- Lars
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