linux-kernel - Re: [PATCH v7 1/6] mfd: max8997: Use regmap to access registers

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Date:	Thu, 02 Jun 2016 09:08:54 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Kukjin Kim <kgene@...nel.org>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Richard Purdie <rpurdie@...ys.net>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-leds@...r.kernel.org, linux-pm@...r.kernel.org,
	r.baldyga@...kerion.com,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v7 1/6] mfd: max8997: Use regmap to access registers

On 06/02/2016 06:43 AM, Krzysztof Kozlowski wrote:
> On 06/01/2016 01:37 PM, Jacek Anaszewski wrote:
>> Hi Krzysztof,
>>
>> One thing drew my attention while reviewing this again:
>> max8997_led_brightness_set() can sleep, but the brightness_set
>> op it is assigned to must not sleep. At the time when this driver was
>> merged we were delegating brightness setting to workqueues task
>> in LED class drivers that can sleep during this call.
>> This must have been overlooked, which is even more likely, taking into
>> account that the initial patch doesn't have LED maintainer's ack.
>>
>> The non-sleeping requirement is motivated by the fact that brightness
>> can be set from softirq context, e.g. when timer trigger is enabled.
>>
>> Currently LED class drivers don't have to use workqueue on their own,
>> but are required to use brightness_set_blocking op instead of
>> brightness_set if they can sleep while setting brightness.
>>
>> Apart of that, I think that operations in max8997_led_brightness_set()
>> should be protected with mutex to assure leaving the device in
>> a consistent state in case of concurrent calls.
>>
>> I am aware that this is out of this patch scope, but I'd be grateful
>> if you could apply those changes and test them on hardware if you have
>> an access to.
>
> The problem you mention existed before the patch. It was using sleeping
> primitives (mutex) before adding regmap so I understand you don't have
> anything against this patch, right?

Right, I just wanted to indicate the problem. The patch itself is ok.

> I can fix the issue but it will be a little bit trickier because I don't
> have the hardware. Other guys in the team tested the patchset for me so
> I rely on them in that matter. Anyway I'll work on it.

Ack.

-- 
Best regards,
Jacek Anaszewski