lkml.org 
[lkml]   [2017]   [Nov]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [alsa-devel] [PATCH 2/2] ASoC: fsl_ssi: serialize AC'97 register access operations
On Mon, Nov 20, 2017 at 11:16:07PM +0100, Maciej S. Szmigiero wrote:
> AC'97 register access operations (both read and write) on SSI use a one,
> shared set of SSI registers for AC'97 register address and data.
> This means that only one such access is possible at a time and so all these
> operations need to be serialized.
>
> Since an AC'97 register access operation in this driver takes 100us+ let's
> use a mutex for this.
>
> Use this opportunity to also change a default value returned from AC'97
> register read function from -1 to 0, since that's what AC'97 specs require
> to be returned when unknown / undefined registers are read.
>
> Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>

> static unsigned short fsl_ssi_ac97_read(struct snd_ac97 *ac97,
> @@ -1287,16 +1295,18 @@ static unsigned short fsl_ssi_ac97_read(struct snd_ac97 *ac97,
> {
> struct regmap *regs = fsl_ac97_data->regs;
>
> - unsigned short val = -1;
> + unsigned short val = 0;
> u32 reg_val;
> unsigned int lreg;
> int ret;
>
> + mutex_lock(&fsl_ac97_data->ac97_reg_lock);
> +
> ret = clk_prepare_enable(fsl_ac97_data->clk);
> if (ret) {
> pr_err("ac97 read clk_prepare_enable failed: %d\n",
> ret);
> - return -1;
> + goto ret_unlock;

It will return val (== 0) in this case. Will this be correctly
handled by callers? I find sound/ac97/bus.c checks if ret < 0
for ops->read().

So it might be better to add "val = ret;" before goto? Or use
val instead of ret directly?

> }
>
> lreg = (reg & 0x7f) << 12;
> @@ -1311,6 +1321,8 @@ static unsigned short fsl_ssi_ac97_read(struct snd_ac97 *ac97,
>
> clk_disable_unprepare(fsl_ac97_data->clk);
>
> +ret_unlock:
> + mutex_unlock(&fsl_ac97_data->ac97_reg_lock);
> return val;
> }

\
 
 \ /
  Last update: 2017-11-21 02:53    [W:0.051 / U:4.260 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site