linux-kernel - Re: [PATCH v8 1/2] PWM: atmel-pwm: add PWM controller 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]

Date:	Wed, 4 Dec 2013 11:03:41 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Bo Shen <voice.shen@...el.com>
Cc:	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
	nicolas.ferre@...el.com, linux-kernel@...r.kernel.org,
	alexandre.belloni@...e-electrons.com, galak@...eaurora.org,
	plagnioj@...osoft.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 1/2] PWM: atmel-pwm: add PWM controller driver

On Wed, Dec 04, 2013 at 10:59:46AM +0800, Bo Shen wrote:
> Hi Thierry,
> 
> On 12/03/2013 05:43 PM, Thierry Reding wrote:
> >On Tue, Dec 03, 2013 at 11:09:12AM +0800, Bo Shen wrote:
> >>On 12/02/2013 06:59 PM, Thierry Reding wrote:
> >>>On Mon, Nov 18, 2013 at 05:13:21PM +0800, Bo Shen wrote:
> >[...]
> >>>>diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> >[...]
> >>>>+	/* Calculate the period cycles */
> >>>>+	while (div > PWM_MAX_PRD) {
> >>>>+		div = clk_rate / (1 << pres);
> >>>>+		div = div * period_ns;
> >>>>+		/* 1/Hz = 100000000 ns */
> >>>
> >>>I don't think that comment is needed.
> >>
> >>This is asked to be added.
> >>And, I think keep it and it won't hurt, what do you think?
> >
> >I think it's obvious that you're converting from nanoseconds because of
> >the _ns prefix in period_ns. But if somebody requested this and everyone
> >else thinks it's useful, I'm okay with keeping it.
> >
> >>>>+	if (test_bit(PWMF_ENABLED, &pwm->flags)) {
> >>>>+		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CDTYUPD, dty);
> >>>>+	} else {
> >>>>+		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CDTY, dty);
> >>>>+		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWMV2_CPRD, prd);
> >>>>+	}
> >>>>+}
> >>>
> >>>Neither version 1 nor version 2 seem to be able to change the period
> >>>while the channel is enabled. Perhaps that should be checked for in
> >>>atmel_pwm_config() and an error (-EBUSY) returned?
> >>
> >>The period is configured in dt in device tree, or platform data in non
> >>device tree. Nowhere will update period. So, not code to update period.
> >>Am I right? If not, please figure out.
> >
> >The .config() operation allows the period to be specified. Just because
> >nobody currently changes it at runtime doesn't mean it can't be done.
> >
> >It is also possible that whoever wrote the device tree or platform data
> >didn't know that the period must be the same for all PWM channels and
> >therefore might use different values. If you check for this, at least
> >they'll notice. If you don't check for it, then they may end up having
> >the period reconfigured behind their backs, which may cause parts of
> >their setup to behave unexpectedly.
> 
> Thanks for this information.
> I will add code for changing period.

Just to clarify: I wouldn't want this code to allow changing the period
but rather reject incompatible changes to the period with an error code.

Thierry

Content of type "application/pgp-signature" skipped