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

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Message-ID: <20221205160328.wn4rcs6uxuuaxftd@pengutronix.de>
Date:   Mon, 5 Dec 2022 17:03:28 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Conor Dooley <conor@...nel.org>,
        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 03:21:55PM +0000, Conor Dooley wrote:
> I came into work today thinking that I could just rebase on top of your
> patchset and send out a v13, but that was unfortunately not the case :/
> 
> So uh, it turns out that I was wrong about the behaviour of the
> sync_update register's bit.
> It turns out that that bit holds it's value until the IP block is reset,
> and /does not/ get cleared at the start of the next period.
> I'm really not sure how it worked when I tested the other week [0], so I
> spent the first half of the day trying to figure out what on earth had
> happened to my FPGA image. I must've picked the wrong image when I went
> to test it the other week that had the wrong configuration somehow.
> 
> As a result, I've gone and hacked up another way of transferring the
> burden of waiting - setting a timer for the period, backed by a
> completion. get_state() and apply() now both check for the completion
> and time out otherwise. I'm half tempted to tack RFC back onto the
> series as I have not really messed with timers at all before and may
> have done something off the wall.
> 
> I pushed it out (see [1] in case you'd like to look) so that the bots
> can have a play with it, since it'll be a few weeks before I'll have a
> chance to properly test that I've broken nothing with this.

I didn't look, but I'm convinced you don't need a timer. Something like
the following should work, shouldn't it?:

 - 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.
 
Best regards
Uwe



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

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