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

[Paul Cercueil <paul@crapouillou.net>]

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>

Reviewed-by: Paul Cercueil <paul@crapouillou.net>

> ---
> 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?
> 
> Best regards
> Uwe
> 
>  drivers/pwm/pwm-jz4740.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
> index f901e8a0d33d..9d444d012f92 100644
> --- a/drivers/pwm/pwm-jz4740.c
> +++ b/drivers/pwm/pwm-jz4740.c
> @@ -2,6 +2,11 @@
>  /*
>   *  Copyright (C) 2010, Lars-Peter Clausen <lars@metafoo.de>
>   *  JZ4740 platform PWM support
> + *
> + * Limitations:
> + * - The .apply callback doesn't complete the currently running 
> period before
> + *   reconfiguring the hardware.
> + * - Each period starts with the inactive part.
>   */
> 
>  #include <linux/clk.h>
> --
> 2.20.1
>