linux-kernel - Re: [PATCH v5 2/2] pwm: Add clock based PWM output driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20220219101049.erwzy5mpmsfgcwjy@pengutronix.de>
Date:   Sat, 19 Feb 2022 11:10:49 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Nikita Travkin <nikita@...n.ru>
Cc:     thierry.reding@...il.com, lee.jones@...aro.org, robh+dt@...nel.org,
        sboyd@...nel.org, krzk@...nel.org, linus.walleij@...aro.org,
        masneyb@...tation.org, sean.anderson@...o.com,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v5 2/2] pwm: Add clock based PWM output driver

Hello,

On Sat, Feb 19, 2022 at 11:46:31AM +0500, Nikita Travkin wrote:
> Uwe Kleine-König писал(а) 14.02.2022 23:43:
> > On Sat, Feb 12, 2022 at 09:23:42PM +0500, Nikita Travkin wrote:
> >> + * Limitations:
> >> + * - Glitches are possible when new pwm state is applied.
> >> + * - Due to the fact that exact behavior depends on the underlying
> >> + *   clock driver, various limitations are possible.
> >> + * - Period depends on the clock and, in general, not guaranteed.
> > 
> > This sentence is broken.
> > 
> 
> Here what I mean is that the clock driver might e.g. have a lookup table
> for some rates and will only set one close to the requested ones.
> (Extreme scenario is that only one rate is allowed in the lookup table,
> which is a real possibility for some platforms that I think this driver
> will be used with, the lookup may need to be changed for those clocks)
> 
> I will reword this like:
> 
>   Some clock drivers may only pick the closest available rate
>   and not the exact requested one. Because of this, exact period
>   is not guaranteed.

That there is no exact match is quite normal also for dedicated PWM
HW blocks. So I think the second item in your list is good enough to
cover the non-existing guaranteed for period and glitches.

Best regards
Uwe

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

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)