linux-kernel - Re: [RFC PATCH 17/40] soundwire: bus: use runtime_pm_get

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Message-ID: <45a912c5-134b-8642-70ef-8c1060389300@linux.intel.com>
Date:   Fri, 26 Jul 2019 13:08:57 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     alsa-devel@...a-project.org
Cc:     linux-kernel@...r.kernel.org, tiwai@...e.de, broonie@...nel.org,
        vkoul@...nel.org, gregkh@...uxfoundation.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, slawomir.blauciak@...el.com,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH 17/40] soundwire: bus: use runtime_pm_get_sync/pm when
 enabled

This thread became unreadable with interleaved top-posting, allow me 
restate the options and ask PM folks what they think

On 7/25/19 6:40 PM, Pierre-Louis Bossart wrote:
> Not all platforms support runtime_pm for now, let's use runtime_pm
> only when enabled.
> 
> Suggested-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> ---
>   drivers/soundwire/bus.c | 25 ++++++++++++++++---------
>   1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> index 5ad4109dc72f..0a45dc5713df 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -332,12 +332,16 @@ int sdw_nread(struct sdw_slave *slave, u32 addr, size_t count, u8 *val)
>   	if (ret < 0)
>   		return ret;
>   
> -	ret = pm_runtime_get_sync(slave->bus->dev);
> -	if (ret < 0)
> -		return ret;
> +	if (pm_runtime_enabled(slave->bus->dev)) {
> +		ret = pm_runtime_get_sync(slave->bus->dev);
> +		if (ret < 0)
> +			return ret;
> +	}
>   
>   	ret = sdw_transfer(slave->bus, &msg);
> -	pm_runtime_put(slave->bus->dev);
> +
> +	if (pm_runtime_enabled(slave->bus->dev))
> +		pm_runtime_put(slave->bus->dev);

This is option1: we explicitly test if pm_runtime is enabled before 
calling _get_sync() and _put()

option2 (suggested by Jan Kotas): catch the -EACCESS error code

  	ret = pm_runtime_get_sync(slave->bus->dev);
-	if (ret < 0)
+	if (ret < 0 && ret != -EACCES)
  		return ret;

option3: ignore the return value as done in quite a few drivers

Are there any other options? I am personally surprised this is not 
handled in the pm_runtime core, not sure why users need to test for this?

Thanks
Pierre