From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thierry Reding Date: Mon, 05 Oct 2015 14:07:41 +0000 Subject: Re: [PATCH] Revert "backlight: pwm: Handle EPROBE_DEFER while requesting the PWM" Message-Id: <20151005140741.GA10625@ulmo> MIME-Version: 1 Content-Type: multipart/mixed; boundary="17pEHd4RhPHOinZp" List-Id: References: <1443295482-18687-1-git-send-email-robert.jarzmik@free.fr> <87bncjemdk.fsf@belgarion.home> <560CE816.1060307@atmel.com> <20151005093543.GB30219@ulmo> <20151005131912.4da38169@bbrezillon> <20151005125803.GA30025@ulmo> <20151005153024.3a245b0b@bbrezillon> In-Reply-To: <20151005153024.3a245b0b@bbrezillon> To: Boris Brezillon Cc: Nicolas Ferre , Robert Jarzmik , linux-pwm@vger.kernel.org, Alexandre Belloni , Jingoo Han , Lee Jones , Jean-Christophe Plagniol-Villard , Tomi Valkeinen , linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org --17pEHd4RhPHOinZp Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Oct 05, 2015 at 03:30:24PM +0200, Boris Brezillon wrote: > On Mon, 5 Oct 2015 14:58:03 +0200 > Thierry Reding wrote: >=20 > > On Mon, Oct 05, 2015 at 01:19:12PM +0200, Boris Brezillon wrote: > > > Hi Thierry, > > >=20 > > > On Mon, 5 Oct 2015 11:35:43 +0200 > > > Thierry Reding wrote: > > >=20 > > > > On Thu, Oct 01, 2015 at 10:00:22AM +0200, Nicolas Ferre wrote: > > > > > Le 30/09/2015 21:29, Robert Jarzmik a =C3=A9crit : > > > > > > Robert Jarzmik writes: > > > > > >=20 > > > > > >> This reverts commit 68feaca0b13e453aa14ee064c1736202b48b342f. > > > > > >> This commit breaks legacy platforms, for which : > > > > > >> (a) no pwm table is added (legacy platforms) > > > > > >> (b) in this case, in pwm_get(), pmw_lookup_list is empty, and= therefore > > > > > >> chosen =3D=3D NULL, and therefore pwm_get() returns NULL,= and pwm_get() > > > > > >> returns -EPROBE_DEFER > > > > > >> (c) as a consequence, this code is unreachable in pwm_bl.c : > > > > > >> if (IS_ERR(pb->pwm)) { > > > > > >> ret =3D PTR_ERR(pb->pwm); > > > > > >> dev_info(&pdev->dev, "%s:%d(): %d\n", __func__, __LINE__, re= t); > > > > > >> if (ret =3D=3D -EPROBE_DEFER) > > > > > >> goto err_alloc; > > > > > >> > > > > > >> dev_err(&pdev->dev, "unable to request PWM, trying legacy AP= I\n"); > > > > > >> pb->legacy =3D true; > > > > > >> pb->pwm =3D pwm_request(data->pwm_id, "pwm-backlight"); > > > > > >> > > > > > >> As this code is unreachable, all legacy platforms relying on p= wm_id are > > > > > >> broken, amongst which pxa have been tested as broken. > > > > > >> > > > > > >> Signed-off-by: Robert Jarzmik > > > > > > Thierry, would you have a look please ? > > > > > > As I said before, all legacy platform relying on pwm_id are bro= ken. I'd like to > > > > > > be sure this lands in the next -rc series. > > > > >=20 > > > > > Well, as I answered on the linux-pwm mailing-list (I was not in c= opy) here: > > > > > http://article.gmane.org/gmane.linux.pwm/2744 > > > > > I wonder if it's not easier to fix the platforms and add the pwm = tables... > > > > >=20 > > > > > Otherwise, Boris proposed this fix: > > > > > 8<----------------------------------------------------------- > > > > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/bac= klight/pwm_bl.c > > > > > index eff379b..00483d4 100644 > > > > > --- a/drivers/video/backlight/pwm_bl.c > > > > > +++ b/drivers/video/backlight/pwm_bl.c > > > > > @@ -273,15 +273,15 @@ static int pwm_backlight_probe(struct platf= orm_device *pdev) > > > > > pb->pwm =3D devm_pwm_get(&pdev->dev, NULL); > > > > > if (IS_ERR(pb->pwm)) { > > > > > ret =3D PTR_ERR(pb->pwm); > > > > > - if (ret =3D=3D -EPROBE_DEFER) > > > > > - goto err_alloc; > > > > > =20 > > > > > dev_err(&pdev->dev, "unable to request PWM, trying legacy API\= n"); > > > > > pb->legacy =3D true; > > > > > pb->pwm =3D pwm_request(data->pwm_id, "pwm-backlight"); > > > > > if (IS_ERR(pb->pwm)) { > > > > > dev_err(&pdev->dev, "unable to request legacy PWM\n"); > > > > > - ret =3D PTR_ERR(pb->pwm); > > > > > + if (ret !=3D -EPROBE_DEFER) > > > > > + ret =3D PTR_ERR(pb->pwm); > > > > > + > > > > > goto err_alloc; > > > > > } > > > > > } > > > > >=20 > > > > > which is not tested and may add an extra non-valid error log. > > > >=20 > > > > This is a little risky in my opinion. Not only does it print two er= ror > > > > messages for non-legacy platforms (that would be another regression= if > > > > you want to be nit-picking), but it is subtly buggy. If you have a > > > > system with multiple PWM providers, you could end up failing the fi= rst > > > > pwm_get() with -EPROBE_DEFER but then continue to the legacy case, = and > > > > this could succeed because data->pwm_id =3D=3D 0, and that other pr= ovider > > > > could be exporting the PWM with this ID. If I remember correctly th= is > > > > was one of the reasons why the offending commit was merged in the f= irst > > > > place. > > >=20 > > > Just for the record, when I proposed this fix to Nicolas, I clearly > > > stated that this was not the way to go, and that fixing the offending > > > platforms to use PWM lookup table was the only sane solution, though I > > > didn't thought about the invalid PWM id case leading to buggy behavio= r. > >=20 > > As chance would have it, this bubbled to the top of my inbox today: > >=20 > > http://patchwork.ozlabs.org/patch/483993/ >=20 > AFAICT, this is not valid either. This patch is assuming -EPROBE_DEFER > can only be returned in the DT case, which is not the case: it is also > returned if the PWMs were declared with a lookup table but the driver > is not registered yet (module not loaded, or driver registration > taking place after the PWM backlight driver). Right, the non-DT, slightly less legacy case... > If we were about to differentiate the missing PWM definition from > the missing driver case, we should do something like this [1]. >=20 > Best Regards, >=20 > Boris >=20 > [1]http://code.bulix.org/2oozbq-89125 Haha, I came up with exactly this earlier and I've been trying to think of ways in which it could potentially break. Thierry --- >8 --- =46rom f7fee34e0c414b4268c59e97937c51e0c91a74cf Mon Sep 17 00:00:00 2001 =46rom: Thierry Reding Date: Mon, 5 Oct 2015 14:38:32 +0200 Subject: [PATCH] pwm: Return -ENODEV if no PWM lookup match is found When looking up a PWM using the lookup table, assume that all entries will have been added already, so failure to find a match means that no corresponding entry has been registered. This fixes an issue where -EPROBE_DEFER would be returned if the PWM lookup table is empty. After this fix, -EPROBE_DEFER is reserved for situations where no provider has yet registered for a matching entry. Signed-off-by: Thierry Reding --- drivers/pwm/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c index 3f9df3ea3350..94e5af123660 100644 --- a/drivers/pwm/core.c +++ b/drivers/pwm/core.c @@ -719,8 +719,10 @@ struct pwm_device *pwm_get(struct device *dev, const c= har *con_id) } } =20 - if (!chosen) + if (!chosen) { + pwm =3D ERR_PTR(-ENODEV); goto out; + } =20 chip =3D pwmchip_find_by_name(chosen->provider); if (!chip) --=20 2.5.0 --17pEHd4RhPHOinZp Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAABCAAGBQJWEoQqAAoJEN0jrNd/PrOhW5cQAIgPfcL2ql/6R+x+2kd0sy0L 59uNN/haZAUJGSYjWW3OLZzwfDVk09Is87RXkp6/FCQg63AA4NeowT5ktTlp9Vmx A/So4zRGvAKQh5WGGWjOf9BeRE9AyOrLsIdT6S7BK+pj6J+BbkDC/YdwSJpMrWGC afexVTtIXLgvLzbkWtHf52MPJ/3mLHFuJD5A+PwfhVYkgvSqLHvVtirmPdw8iAjm heZZWVHF9Pj/poI8BWbmbcX6zWvgMP1seXo5XZrqr/3jqarYVrEM1utT8qNjTilr KnG3q3GRKVI6Z3rLxw6xz67qgweQcdJUFoTnPHTKhiPJp7InKq1BTcNleKVJujzW U/ocGc4JmBsknaG9dey2TO0zyNv3CiWMQgNuqFdwbQ//onj0keiNIziCnwyupZyw xoAN6+EDpuBICKOLmaLMQmQOs1AYNDa/ZXaAmAng+QSrZOjN1U3If+rtj8GIwtmy 1gPtg2azTwX/qWzq222Y77ErAcQsDzyO/MLM6QHO77MyEuUmyC0UM4wiUFO3Xz2K dRf+kFPcOW4hOqxMwIhv8q2b3IIoHWEIPaqHkxyC0HHx3SmmKS7kK75CcGVRi+qy 7mOpo6k5GoCgwvHK9ZOhybFcEEgy8Higeq7IlLuvBwAM7HovWmx8lQyjSupKTUqb DeCfsKLZSXqp6AQNdNK9 =oRY5 -----END PGP SIGNATURE----- --17pEHd4RhPHOinZp--