linux-kernel - Re: [PATCH v12 1/2] pwm: add microchip soft ip corePWM driver

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Date:   Mon, 5 Dec 2022 19:13:48 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Conor Dooley <conor@...nel.org>
Cc:     Conor Dooley <conor.dooley@...rochip.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v12 1/2] pwm: add microchip soft ip corePWM driver

Hello Conor,

On Mon, Dec 05, 2022 at 05:13:42PM +0000, Conor Dooley wrote:
> Figured I was better off doing something quickly & asking rather than
> polishing only to find out it was disliked ;)

:-)

> >  - in .apply() check the current time, add the current period and store
> >    the result to ddata->updatetimestamp
> >  - in .get_state do:
> >      if (current_time >= ddata->updatetimestamp)
> >        process fine
> >      else:
> >        timeout (or wait until ddata->updatetimestamp?)
> > 
> > Actually I'd prefer to wait instead of -ETIMEOUT.
> 
> Prefer to wait in get_state() or in both it & apply()?

Prefer to wait where it's necessary ...

> Depending on how far away updatetimestamp is, would we still not want to
> time out if it is going to be a long time, no?

I'd prefer a slow but right value over a quick error.

The sun4i driver has in its .apply():

        /* We need a full period to elapse before disabling the channel. */
        delay_us = DIV_ROUND_UP_ULL(cstate.period, NSEC_PER_USEC);
        if ((delay_us / 500) > MAX_UDELAY_MS)
                msleep(delay_us / 1000 + 1);
        else
                usleep_range(delay_us, delay_us * 2);

so it's at least not new in general to have a waiting time in O(period).

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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