linux-kernel - Re: [PATCH 3/4] soundwire: debugfs: Switch to sdw_read_no

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Date:   Mon, 14 Nov 2022 10:14:19 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>, vkoul@...nel.org
Cc:     yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com
Subject: Re: [PATCH 3/4] soundwire: debugfs: Switch to sdw_read_no_pm



On 11/14/22 04:29, Charles Keepax wrote:
> It is rather inefficient to be constantly enabling/disabling the PM
> runtime as we print out each individual register, switch to holding a PM
> runtime reference across the whole register output.

the change is good, but technically the pm_runtime resume happens for
the first read and suspend with a delay if use_autosuspend() is enabled,
so presumably we'll see the same number of resume/suspend with the
existing code and the suggested change.

Maybe update the commit message to mention that we constantly change
reference counts, as you did in the next patch?

> 
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> ---
>  drivers/soundwire/debugfs.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/soundwire/debugfs.c b/drivers/soundwire/debugfs.c
> index 49900cd207bc7..0718e9cda138a 100644
> --- a/drivers/soundwire/debugfs.c
> +++ b/drivers/soundwire/debugfs.c
> @@ -4,6 +4,7 @@
>  #include <linux/device.h>
>  #include <linux/debugfs.h>
>  #include <linux/mod_devicetable.h>
> +#include <linux/pm_runtime.h>
>  #include <linux/slab.h>
>  #include <linux/soundwire/sdw.h>
>  #include <linux/soundwire/sdw_registers.h>
> @@ -35,7 +36,7 @@ static ssize_t sdw_sprintf(struct sdw_slave *slave,
>  {
>  	int value;
>  
> -	value = sdw_read(slave, reg);
> +	value = sdw_read_no_pm(slave, reg);
>  
>  	if (value < 0)
>  		return scnprintf(buf + pos, RD_BUF - pos, "%3x\tXX\n", reg);
> @@ -55,6 +56,10 @@ static int sdw_slave_reg_show(struct seq_file *s_file, void *data)
>  	if (!buf)
>  		return -ENOMEM;
>  
> +	ret = pm_runtime_resume_and_get(&slave->dev);
> +	if (ret < 0 && ret != -EACCES)
> +		return ret;
> +
>  	ret = scnprintf(buf, RD_BUF, "Register  Value\n");
>  
>  	/* DP0 non-banked registers */
> @@ -112,6 +117,10 @@ static int sdw_slave_reg_show(struct seq_file *s_file, void *data)
>  	}
>  
>  	seq_printf(s_file, "%s", buf);
> +
> +	pm_runtime_mark_last_busy(&slave->dev);
> +	pm_runtime_put(&slave->dev);
> +
>  	kfree(buf);
>  
>  	return 0;