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[217.229.28.220]) by smtp.gmail.com with ESMTPSA id m11sm12835978wmf.9.2020.04.03.12.44.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Apr 2020 12:44:26 -0700 (PDT) Date: Fri, 3 Apr 2020 21:44:25 +0200 From: Thierry Reding To: Clemens Gruber Cc: linux-pwm@vger.kernel.org, Andy Shevchenko , Matthias Schiffer , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , linux-kernel@vger.kernel.org, Sven Van Asbroeck , YueHaibing , Mika Westerberg Subject: Re: [PATCH v2 REBASED] pwm: pca9685: fix pwm/gpio inter-operation Message-ID: <20200403194425.GC201060@ulmo> References: <20200401170106.134037-1-clemens.gruber@pqgruber.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="lCAWRPmW1mITcIfM" Content-Disposition: inline In-Reply-To: <20200401170106.134037-1-clemens.gruber@pqgruber.com> User-Agent: Mutt/1.13.1 (2019-12-14) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --lCAWRPmW1mITcIfM Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Apr 01, 2020 at 07:01:06PM +0200, Clemens Gruber wrote: > From: Sven Van Asbroeck >=20 > This driver allows pwms to be requested as gpios via gpiolib. > Obviously, it should not be allowed to request a gpio when its > corresponding pwm is already requested (and vice versa). > So it requires some exclusion code. >=20 > Given that the pwm and gpio cores are not synchronized with > respect to each other, this exclusion code will also require > proper synchronization. >=20 > Such a mechanism was in place, but was inadvertently removed > by Uwe's clean-up patch. >=20 > Upon revisiting the synchronization mechanism, we found that > theoretically, it could allow two threads to successfully > request conflicting pwms / gpios. >=20 > Replace with a bitmap which tracks pwm in-use, plus a mutex. > As long as pwm and gpio's respective request/free functions > modify the in-use bitmap while holding the mutex, proper > synchronization will be guaranteed. >=20 > Reported-by: YueHaibing > Fixes: e926b12c611c ("pwm: Clear chip_data in pwm_put()") > Cc: Mika Westerberg > Cc: Uwe Kleine-K=C3=B6nig > Cc: YueHaibing > Link: https://lkml.org/lkml/2019/5/31/963 > Signed-off-by: Sven Van Asbroeck > Reviewed-by: Mika Westerberg > Tested-by: Clemens Gruber > [cg: Tested on an i.MX6Q board with two NXP PCA9685 chips] >=20 > --- > drivers/pwm/pwm-pca9685.c | 85 ++++++++++++++++++++++----------------- > 1 file changed, 48 insertions(+), 37 deletions(-) Applied, thanks. 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