From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751909AbcFUV3f (ORCPT ); Tue, 21 Jun 2016 17:29:35 -0400 Received: from down.free-electrons.com ([37.187.137.238]:45936 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751756AbcFUV3d (ORCPT ); Tue, 21 Jun 2016 17:29:33 -0400 Date: Tue, 21 Jun 2016 23:22:58 +0200 From: Boris Brezillon To: Brian Norris Cc: Geert Uytterhoeven , Thierry Reding , Linux PWM List , "linux-kernel@vger.kernel.org" , Brian Norris , Doug Anderson , linux-renesas-soc@vger.kernel.org, Laurent Pinchart Subject: Re: [PATCH v2] pwm: improve args checking in pwm_apply_state() Message-ID: <20160621232258.62105f7a@bbrezillon> In-Reply-To: <20160621183730.GA130978@google.com> References: <1464367549-111530-1-git-send-email-briannorris@chromium.org> <20160621183730.GA130978@google.com> Organization: Free Electrons X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 21 Jun 2016 11:37:31 -0700 Brian Norris wrote: > Hi Geert, > > On Tue, Jun 21, 2016 at 04:42:04PM +0200, Geert Uytterhoeven wrote: > > On Fri, May 27, 2016 at 6:45 PM, Brian Norris wrote: > > > It seems like in the process of refactoring pwm_config() to utilize the > > > newly-introduced pwm_apply_state() API, some args/bounds checking was > > > dropped. > > > > > > In particular, I noted that we are now allowing invalid period > > > selections. e.g.: > > > > > > # echo 1 > /sys/class/pwm/pwmchip0/export > > > # cat /sys/class/pwm/pwmchip0/pwm1/period > > > 100 > > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle > > > [... driver may or may not reject the value, or trigger some logic bug ...] > > > > > > It's better to see: > > > > > > # echo 1 > /sys/class/pwm/pwmchip0/export > > > # cat /sys/class/pwm/pwmchip0/pwm1/period > > > 100 > > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle > > > -bash: echo: write error: Invalid argument > > > > > > This patch reintroduces some bounds checks in both pwm_config() (for its > > > signed parameters; we don't want to convert negative values into large > > > unsigned values) and in pwm_apply_state() (which fix the above described > > > behavior, as well as other potential API misuses). > > > > > > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") > > > Signed-off-by: Brian Norris > > > --- > > > v2: > > > * changed subject, as this covers more scope now > > > * add Fixes tag, as this is a v4.7-rc regression > > > * add more bounds/args checks in pwm_apply_state() and pwm_config() > > > > > > drivers/pwm/core.c | 3 ++- > > > include/linux/pwm.h | 3 +++ > > > 2 files changed, 5 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > > > index dba3843c53b8..ed337a8c34ab 100644 > > > --- a/drivers/pwm/core.c > > > +++ b/drivers/pwm/core.c > > > @@ -457,7 +457,8 @@ int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state) > > > { > > > int err; > > > > > > - if (!pwm) > > > + if (!pwm || !state || !state->period || > > > + state->duty_cycle > state->period) > > > return -EINVAL; > > > > This check breaks the LCD backlight on r8a7740/armadillo. > > Apparently both period and duty_cycle are zero during the first invocation. > > Later, these are initialized from DT, cfr. > > > > pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>; > > > > in arch/arm/boot/dts/r8a7740-armadillo800eva.dts. > > Hmm, this isn't super obvious how to best fix. On one hand, the > pwm_config() API used to reject period<=0, but on the other hand, I > think its replacement (pwm_apply_state()) is getting used in more places > than it used to be, and not all of them are really handling the "atomic > update" concept yet. Seems like a product of Boris's multi-phase attempt > to convert the PWM APIs to support atomic updates -- and many users > haven't really converted yet. > > > With added debug printing, the difference between failure and success is: > > > > renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered > > tpu_pwm_request:223 > > pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0 > > +Ignoring failure > > +pwm_apply_state:479: polarity 0 -> 1 > > +tpu_pwm_set_polarity:343 > > +pwm_apply_state:502: period 0 -> 0 > > +pwm_apply_state:503: duty_cycle 0 -> 0 > > +pwm_apply_state:516: enabled 0 -> 0 > > pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333 > > pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333 > > -pwm_apply_state:479: polarity 0 -> 0 > > +pwm_apply_state:479: polarity 1 -> 1 > > pwm_apply_state:502: period 0 -> 33333 > > pwm_apply_state:503: duty_cycle 0 -> 33333 > > tpu_pwm_config:267 > > pwm_apply_state:516: enabled 0 -> 0 > > pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333 > > -pwm_apply_state:479: polarity 0 -> 0 > > +pwm_apply_state:479: polarity 1 -> 1 > > pwm_apply_state:502: period 33333 -> 33333 > > pwm_apply_state:503: duty_cycle 33333 -> 33333 > > pwm_apply_state:516: enabled 0 -> 1 > > tpu_pwm_enable:354 > > I'm not sure I 100% understand this debug log, but I think maybe the > problem is in pwm_apply_args(), which calls pwm_disable() and > pwm_set_polarity() sequentially, without ever configuring a period? What > if pwm_apply_args() were to configure the period for us? > > Boris, any thoughts? I think this is partly caused by this commit: a8c3862551e0 ("pwm: Keep PWM state in sync with hardware state") But again, we need that one if we don't want to override the current PWM period with the pwm_args one when the driver support hardware readout. This leaves 2 choices: 1/ assign the period to pargs->period if ->get_state() is not implemented 2/ remove the !period check in pwm_apply_state() when state->enabled is false (do we really care if period = 0 when all we want to do is disable the PWM?) Thierry, what's you're opinion.