linux-kernel - Re: [linux-sunxi] [RFC PATCH 4/4] pwm: sun4i: Delay after writing the period

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Message-ID: <fd36eddb87b529498e0429afe3521da7@pascalroeleven.nl>
Date:   Wed, 22 Apr 2020 10:40:11 +0200
From:   Pascal Roeleven <dev@...calroeleven.nl>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-pwm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [linux-sunxi] [RFC PATCH 4/4] pwm: sun4i: Delay after writing the
 period

On 2020-04-22 05:43, Samuel Holland wrote:
> Hello Pascal,
> 
> On 3/17/20 10:59 AM, Pascal Roeleven wrote:
>> When disabling, ensure the period write is complete before continuing.
>> This fixes an issue on some devices when the write isn't complete 
>> before
>> the panel is turned off but the clock gate is still on.
>> 
>> Signed-off-by: Pascal Roeleven <dev@...calroeleven.nl>
>> ---
>>  drivers/pwm/pwm-sun4i.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>> 
>> diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
>> index a11d00f96..75250fd4c 100644
>> --- a/drivers/pwm/pwm-sun4i.c
>> +++ b/drivers/pwm/pwm-sun4i.c
>> @@ -299,6 +299,10 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, 
>> struct pwm_device *pwm,
>>  	sun4i_pwm_writel(sun4i_pwm, val, PWM_CH_PRD(pwm->hwpwm));
>>  	next_period = jiffies + usecs_to_jiffies(cstate.period / 1000 + 1);
>> 
>> +	/* When disabling, make sure the period register is written first */
>> +	if (!state->enabled && cstate.enabled)
>> +		sun4i_pwm_wait(next_period);
>> +
> 
> It is not visible from the context of this patch, but this call to
> sun4i_pwm_wait() ends up calling msleep() inside a spinlock, which 
> isn't
> allowed. The spinlock should probably be converted to a mutex, 
> considering that
> sun4i_pwm_apply() already sleeps and takes mutexes.
> 
> Regards,
> Samuel
> 

Yes you're right. A different implementation of this patch series is 
being worked on, in which I'll take this into account. Unfortunately I 
have other things to work on at the moment, so it might take a while.

Regards,
Pascal