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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Thu, 5 Mar 2015 17:53:57 +0000
From:	Mark Brown <broonie@...nel.org>
To:	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 Thu, Mar 05, 2015 at 07:35:32PM +0200, Daniel Baluta wrote:

> Is it possible to use regmap_update_bits to update the values
> of some bits in a write only register?

That should work.

> I was hoping that by filling the .reg_defaults field of regmap_config
> the regmap_update_bits function will not try to read the register
> from hardware.

> Instead I think first call of regmap_update_bits will try to read the register
> from hardware, but this fails with -EIO because the register is marked as
> write only.

> Am I doing something wrong?

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...

Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)