linux-kernel - Re: [PATCH v4 2/2] pwm: visconti: Add Toshiba Visconti SoC PWM support

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] [day] [month] [year] [list]

Message-ID: <20210418110718.4zrh665anbz3wmqc@toshiba.co.jp>
Date:   Sun, 18 Apr 2021 20:07:18 +0900
From:   Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>, devicetree@...r.kernel.org,
        linux-pwm@...r.kernel.org, punit1.agrawal@...hiba.co.jp,
        yuji2.ishikawa@...hiba.co.jp, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] pwm: visconti: Add Toshiba Visconti SoC PWM
 support

Hi Uwe,

On Sat, Apr 17, 2021 at 05:50:09PM +0200, Uwe Kleine-König wrote:
> Hello Nobuhiro,
> 
> On Fri, Apr 16, 2021 at 09:15:23PM +0900, Nobuhiro Iwamatsu wrote:
> > > > > For me the critical (and only) difference between "off" and
> > > > > "duty cycle = 0" is that when a new configuration is to be applied. In
> > > > > the "off" state a new period can (and should) start immediately, while
> > > > > with "duty_cycle = 0" the rising edge should be delayed until the
> > > > > currently running period is over.[1]
> > > > > 
> > > > > So the thing to do here (IMHO) is:
> > > > > 
> > > > > Iff with PIPGM_PCSR = 0 configuring a new setting (that is finalized
> > > > > with writing a non-zero value to PIPGM_PCSR) completes the currently
> > > > > running period, then always assume the PWM as enabled.
> > > > 
> > > > Yes, this device works that way.
> > > 
> > > OK, then please use
> > > 
> > > 	state->enabled = true
> > > 
> > > unconditionally in visconti_pwm_get_state().
> > 
> > Please let me check.
> > If I unconditionally add 'state->enabled = true' to visconti_pwm_get_state(),
> > state->enabled is set to true because visconti_pwm_get_state() is called when
> > the device is created (this is when I write the device number to the export of
> > /sys/class/pwm/pwmchip0 ).
> > And since PIPGM_PCSR is 0 in this state, the pulse by PWM is not output.
> 
> A PWM that is currently configured with .enabled = true and .duty_cycle
> = 0 doesn't have a pulse, so this is fine.
> 

I understood, thanks.

> > However, I think this means that the device is working as this driver.
> 
> I don't understand this sentence.

The description of the struct pwm_state says "PWM enabled status".
I thought 'state-> enabled' would hold the working state of the hardware.

> 
> Best regards
> Uwe

Best regards,
  Nobuhiro