linux-kernel - Re: [QUEUED v20160630 1/4] stm class: Add runtime power management handling

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Message-ID: <877fd6snhb.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Thu, 30 Jun 2016 18:30:40 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:	Greg KH <greg@...ah.com>, Chunyan Zhang <zhang.chunyan@...aro.org>,
	laurent.fert@...el.com, yann.fouassier@...el.com,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [QUEUED v20160630 1/4] stm class: Add runtime power management handling

Mathieu Poirier <mathieu.poirier@...aro.org> writes:

> On 30 June 2016 at 06:56, Alexander Shishkin
> <alexander.shishkin@...ux.intel.com> wrote:
>> Currently, there's no runtime pm in stm class devices, which makes it
>> harder for the underlying hardware drivers to handle their power
>> management.
>>
>> This patch applies the following runtime pm policy to stm class devices,
>> which their parents can rely on for their power management tracking:
>>
>>   * device is in use during character device writes,
>>   * delayed autosuspend is used to keep it active between adjacent
>>   writes,
>>   * device is in use while mmio regions are mapped,
>>   * device is is use while any stm_source devices are linked to it.
>>
>> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>> Cc: Chunyan Zhang <zhang.chunyan@...aro.org>
>
> Coresight power management on my Juno board (the only device with an
> STM I have access to) is broken and as such, can't test if this code
> does what is intended.  But theoretically it looks good.

Thanks for taking a look.

> Throughout the driver, wouldn't it be better to use
> pm_runtime_put_sync() rather than autosuspending with a hard coded
> value?

Yeah, the autosuspend is for the char write()ers that are likely to send
multiple consequent write()s, so that we don't have to go in and out of
suspend every time that happens.

Thanks,
--
Alex