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Thu, 05 Jul 2018 23:06:11 -0700 (PDT) Date: Fri, 6 Jul 2018 07:06:09 +0100 From: Lee Jones To: Janusz Krzysztofik Cc: Boris Brezillon , Linus Walleij , linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, Wolfram Sang , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Fabio Estevam , Phil Reid , Lucas Stach , Clemens Gruber , Peter Rosin , patches@opensource.cirrus.com, linux-i2c@vger.kernel.org, ckeepax@opensource.wolfsonmicro.com, rf@opensource.wolfsonmicro.com, broonie@kernel.org Subject: Re: [PATCH] gpiolib: Defer on non-DT find_chip_by_name() failure Message-ID: <20180706060609.GT496@dell> References: <20180703172635.32508-1-jmkrzyszt@gmail.com> <7058252.SGNltMTCCa@z50> <20180705055037.GI496@dell> <1579112.qQSMXVQn9s@z50> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1579112.qQSMXVQn9s@z50> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 05 Jul 2018, Janusz Krzysztofik wrote: > On Thursday, July 5, 2018 7:50:37 AM CEST Lee Jones wrote: > > On Wed, 04 Jul 2018, Janusz Krzysztofik wrote: > > > On Tuesday, July 3, 2018 7:31:41 PM CEST Boris Brezillon wrote: > > > > Hi Janusz, > > > > > > > > On Tue, 3 Jul 2018 19:26:35 +0200 > > > > > > > > Janusz Krzysztofik wrote: > > > > > Avoid replication of error code conversion in non-DT GPIO consumers' > > > > > code by returning -EPROBE_DEFER from gpiod_find() in case a chip > > > > > identified by its label in a registered lookup table is not ready. > > > > > > > > > > See https://lkml.org/lkml/2018/5/30/176 for example case. > > > > > > > > > > Signed-off-by: Janusz Krzysztofik > > > > > --- > > > > > If accepted, please add > > > > > > > > > > Suggested-by: Boris Brezillon > > > > > > > > > > if Boris doesn't mind. > > > > > > > > > > Thanks, > > > > > Janusz > > > > > > > > > > drivers/gpio/gpiolib.c | 13 ++++++++++--- > > > > > 1 file changed, 10 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c > > > > > index e11a3bb03820..15dc77c80328 100644 > > > > > --- a/drivers/gpio/gpiolib.c > > > > > +++ b/drivers/gpio/gpiolib.c > > > > > @@ -3639,9 +3639,16 @@ static struct gpio_desc *gpiod_find(struct > > > > > device > > > > > *dev, const char *con_id,> > > > > > > > > > > chip = find_chip_by_name(p->chip_label); > > > > > > > > > > if (!chip) { > > > > > > > > > > - dev_err(dev, "cannot find GPIO chip %s\n", > > > > > - p->chip_label); > > > > > - return ERR_PTR(-ENODEV); > > > > > + /* > > > > > + * As the lookup table indicates a chip with > > > > > + * p->chip_label should exist, assume it may > > > > > + * still appear latar and let the interested > > > > > > > > > ^ later > > > > > > > > > > + * consumer be probed again or let the Deferred > > > > > + * Probe infrastructure handle the error. > > > > > + */ > > > > > + dev_warn(dev, "cannot find GPIO chip %s, deferring\n", > > > > > + p->chip_label); > > > > > + return ERR_PTR(-EPROBE_DEFER); > > > > > > > > > > } > > > > > > > > > > if (chip->ngpio <= p->chip_hwnum) { > > > > > > > > Looks good otherwise. Let's hope we're not breaking implementations > > > > testing for -ENODEV... > > > > > > I've reviewed them all and found two which I think may be affected: > > > - drivers/mfd/arizona-core.c, > > > - drivers/i2c/busses/i2c-imx.c. > > > As far as I can understand the code, both depend on error != -EPROBE_DEFER > > > in order to continue in degraded mode. I'm adding their maintainers to > > > the loop. > > From a quick glance, the -EPROBE_DEFER handing in Arizona Core appears > > to be correct. Would you mind explaining what your concerns are in > > more detail please? > > Hi > > That's more about handling -ENODEV rather than -EPROBE_DEFER. > > Before the change, if GPIO chip supposed to provide "reset" pin was not ready > during arizona_dev_init(), devm_gpiod_get() returned -ENODEV and device was > initialized in degraded mode, i.e., with no control over the "reset" pin. > After the change, gpiod_get() will return -EPROBE_DEFER in such case and > arizona_dev_init() won't succeed in case the GPIO chip doesn't appear later > for some reason. Yes, I see that now. Thanks for your explanation. I'm bringing in the big guns (CC'ed). -- Lee Jones [李琼斯] Linaro Services Technical Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog