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Date:   Wed, 25 Nov 2020 10:35:28 +0530
From:   Vinod Koul <vkoul@kernel.org>
To:     Bard Liao <yung-chuan.liao@linux.intel.com>
Cc:     alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
        gregkh@linuxfoundation.org, jank@cadence.com,
        srinivas.kandagatla@linaro.org, rander.wang@linux.intel.com,
        ranjani.sridharan@linux.intel.com, hui.wang@canonical.com,
        pierre-louis.bossart@linux.intel.com, sanyog.r.kale@intel.com,
        mengdong.lin@intel.com, bard.liao@intel.com
Subject: Re: [PATCH] soundwire: master: use pm_runtime_set_active() on add
Message-ID: <20201125050528.GC8403@vkoul-mobl>
References: <20201124130742.10986-1-yung-chuan.liao@linux.intel.com>
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On 24-11-20, 21:07, Bard Liao wrote:
> From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> 
> The 'master' device acts as a glue layer used during bus
> initialization only, and it needs to be 'transparent' for pm_runtime
> management. Its behavior should be that it becomes active when one of
> its children becomes active, and suspends when all of its children are
> suspended.
> 
> In our tests on Intel platforms, we routinely see these sort of
> warnings on the initial boot:
> 
> [ 21.447345] rt715 sdw:3:25d:715:0: runtime PM trying to activate
> child device sdw:3:25d:715:0 but parent (sdw-master-3) is not active
> 
> This is root-caused to a missing setup to make the device 'active' on
> probe. Since we don't want the device to remain active forever after
> the probe, the autosuspend configuration is also enabled at the end of
> the probe - the device will actually autosuspend only in the case
> where there are no devices physically attached. In practice, the
> master device will suspend when all its children are no longer active.
> 
> Fixes: bd84256e86ecf ('soundwire: master: enable pm runtime')
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> Reviewed-by: Rander Wang <rander.wang@linux.intel.com>
> Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
> ---
>  drivers/soundwire/master.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/soundwire/master.c b/drivers/soundwire/master.c
> index 3488bb824e84..9b05c9e25ebe 100644
> --- a/drivers/soundwire/master.c
> +++ b/drivers/soundwire/master.c
> @@ -8,6 +8,15 @@
>  #include <linux/soundwire/sdw_type.h>
>  #include "bus.h"
>  
> +/*
> + * The 3s value for autosuspend will only be used if there are no
> + * devices physically attached on a bus segment. In practice enabling
> + * the bus operation will result in children devices become active and
> + * the master device will only suspend when all its children are no
> + * longer active.
> + */
> +#define SDW_MASTER_SUSPEND_DELAY_MS 3000
> +
>  /*
>   * The sysfs for properties reflects the MIPI description as given
>   * in the MIPI DisCo spec
> @@ -154,7 +163,12 @@ int sdw_master_device_add(struct sdw_bus *bus, struct device *parent,
>  	bus->dev = &md->dev;
>  	bus->md = md;
>  
> +	pm_runtime_set_autosuspend_delay(&bus->md->dev, SDW_MASTER_SUSPEND_DELAY_MS);
> +	pm_runtime_use_autosuspend(&bus->md->dev);
> +	pm_runtime_mark_last_busy(&bus->md->dev);
> +	pm_runtime_set_active(&bus->md->dev);
>  	pm_runtime_enable(&bus->md->dev);
> +	pm_runtime_idle(&bus->md->dev);

I understand that this needs to be done somewhere but is the core the
right place. In intel case it maybe a dummy device but other controllers
are real devices and may not support pm.

I think better idea would be to do this in respective driver.. that way
it would be an opt-in for device supporting pm.

Thanks
-- 
~Vinod