Re: [PATCH] pwm: jz4740: document known limitations

[Paul Cercueil <paul@crapouillou.net>]

Le mer. 7 août 2019 à 15:49, Uwe =?iso-8859-1?q?Kleine-K=F6nig?= 
<u.kleine-koenig@pengutronix.de> a écrit :
> On Wed, Aug 07, 2019 at 03:42:31PM +0200, Paul Cercueil wrote:
>> 
>> 
>>  Le mar. 30 juil. 2019 à 14:32, Uwe =?iso-8859-1?q?Kleine-K=F6nig?=
>>  <u.kleine-koenig@pengutronix.de> a écrit :
>>  > The jz4740 PMW implementation doesn't fulfill the (up to now
>>  > insufficiently documented) requirements of the PWM API. At least
>>  > document them in the driver.
>>  >
>>  > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
>>  > ---
>>  > I intended to also add a Link to the reference manual, Paul 
>> suggested to
>>  > use https://zcrc.me/~paul/jz_docs/ in December last year, but this
>>  > stopped to work.
>>  >
>>  > The second item is something I noticed when reading through the 
>> manual,
>>  > but it's not confirmed in practise. A test that this is indeed 
>> the case
>>  > could be done by configuring a long period (say 5s) and a (in
>>  > comparison) small duty-cycle (say 1s). If the pwm output isn't 
>> active
>>  > when the call returns I'd consider this proven.
>>  >
>>  > @Paul: would you mind doing this test?
>> 
>>  You're correct. I configured it for 4s period and 2s duty. After 
>> enabling
>>  the
>>  PWM, it stays LOW for two seconds then switches HIGH for two 
>> seconds.
>> 
>>  That can be corrected, though, by inverting the configured polarity 
>> when the
>>  PWM is running and set "period - duty" as the duty value. I can 
>> make a patch
>>  for that.
> 
> OK. Do you care for documenting the first limitation then, too?
> 
> Or should we apply my patch as is and you remote the second item when
> you fix it?

Yes, just apply the patch, and I'll remove the second comment when I 
send mine.

-Paul


> Best regards
> Uwe
> 
> --
> Pengutronix e.K.                           | Uwe Kleine-König        
>     |
> Industrial Linux Solutions                 | 
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