lkml.org 
[lkml]   [2014]   [Sep]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH V1] ASoC: fsl_ssi: refine ipg clock usage in this module
On Wed, Sep 10, 2014 at 04:12:53PM +0800, Shengjiu Wang wrote:
> > Then we can get a patch like:
> > open() {
> > + clk_prepare_enable();
> > ....
> > }
> >
> > close() {
> > ....
> > + clk_disable_unprepare()
> > }

> what is the open() and close()? do you mean the fsl_ssi_startup()
> and fsl_ssi_shutdown()?

Yea.

> > probe() {
> > clk_get();
> > clk_prepare_enable();
> > ....
> > if (xxx)
> > - goto err_xx;
> > + return ret;
> > ....
> > + clk_disable_unprepare();
> > return 0;
> > -err_xx:
> > - clk_disable_unprepare()
> > }

> If this probe() is fsl_ssi_imx_probe(), I think no need to add
> clk_prepare_enable() or clk_disable_unprepare(), seems there is no
> registers accessing in this probe.

This is trying to be safe, especially for such a driver being used
by multiple platforms. You can omit this as long as the patch can
pass the test on old imx, PowerPC, and AC97 platforms.

>

And another risk just came to my mind is that there would be a
possibility that a machine driver would call set_dai_fmt() early,
after SSI's probe() and before SSI's startup(), if the machine
driver contains dai_fmt assignment in its probe(). Then, without
regmap_mmio_clk(), it'll be tough for us over here because we may
also need to add clock enable/disable for set_dai_fmt/set_sysclk(),
even if there might be still tiny risk that we missed something.

Then there could be a selfish approach to circumvent it is to use
regmap_mmio_clk() with "ipg" at the beginning and call regmap_mmio()
without "ipg" if getting a failed return value from regmap_mmio_clk,
and meanwhile to keep the clock always enabled for the regmap_mmio()
case just like what the current driver is doing. This may result
those non-ipg-clk platforms can't benefit from this refinement
unless they update their DT bindings -- use "ipg" for core clock
This might be the safest and simplest way for us, I'm not sure
everyone would be comfortable with this idea though.

Best regards,
Nicolin


\
 
 \ /
  Last update: 2014-09-10 20:21    [W:0.132 / U:0.580 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site