linux-kernel - Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq

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

Date:   Thu, 7 Sep 2017 14:44:11 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Łukasz Majewski <lukma@...x.de>,
        Timur Tabi <timur@...i.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal
 to system freq

On Tue, Sep 05, 2017 at 10:45:29AM -0700, Nicolin Chen wrote:

> The ipg clock is merely used to access registers, and has nothing
> (directly) to do with external clock outputs. The driver shall not
> change the ipg clock as the system ipg clock (its parent clock)
> might be messed and even system time would get weird -- happened
> once when the fsl_spdif driver used to call clk_set_rate() on its
> ipg clock. Although the clock controller should have some kind of
> protection in my opinion, we just avoid IP clock rate change in all
> audio drivers as well.

Yes, the clock API needs constraints code.

> On the other hand, the sys clock (baudclk in the driver) should be
> configured whenever it's related to external clock outputs. When I
> implemented this set_sysclk() for fsl_ssi.c, I used it to set this
> sys clock (baudclk) by a machine driver, in order to set bit clock.
> Then someone patched the driver by moving all the code to set_bclk()
> to make machine drivers simpler. Now the set_sysclk() is remained
> to give machine drivers a chance to override clock configurations
> in the hw_params(). This could be used in TDM or some other special
> cases (It could also have a purpose for backwards compatibility).

> So here, we should set baudclk (BCLK generator).

No, that's just going to cause confusion - if all the other drivers are
using set_sysclk() to set an input clock rate to the IP rather than an
output clock but your driver does something else then sooner or later
someone will run into trouble with that.  

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)