From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ladislav Michl Date: Sun, 20 May 2018 19:27:05 +0000 Subject: Re: [alsa-devel] [PATCH 5/6] mtd: rawnand: ams-delta: use GPIO lookup table Message-Id: <20180520192705.GA12883@lenoch> List-Id: References: <20180518210954.29044-1-jmkrzyszt@gmail.com> <3427199.r4OBoDP6Xz@z50> <5456625.lDWjtgZygK@z50> In-Reply-To: <5456625.lDWjtgZygK@z50> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Janusz Krzysztofik Cc: Andy Shevchenko , linux-fbdev@vger.kernel.org, ALSA Development Mailing List , Aaro Koskinen , Tony Lindgren , Richard Weinberger , Mark Brown , Dmitry Torokhov , Liam Girdwood , Linux Kernel Mailing List , Peter Ujfalusi , Boris Brezillon , Tomi Valkeinen , "open list:MEMORY TECHNOLOGY..." , linux-arm Mailing List , linux-input , Linux OMAP Mailing List On Sat, May 19, 2018 at 11:55:51PM +0200, Janusz Krzysztofik wrote: > On Saturday, May 19, 2018 8:00:38 PM CEST Andy Shevchenko wrote: > > On Sat, May 19, 2018 at 2:15 AM, Janusz Krzysztofik > wrote: > > > On Friday, May 18, 2018 11:21:14 PM CEST Andy Shevchenko wrote: > > >> On Sat, May 19, 2018 at 12:09 AM, Janusz Krzysztofik > > >> > > >> wrote: > > >> > + gpiod_rdy = devm_gpiod_get_optional(&pdev->dev, "rdy", > > >> > GPIOD_IN); > > >> > + if (!IS_ERR_OR_NULL(gpiod_rdy)) { > > >> > > >> So, is it optional or not at the end? > > >> If it is, why do we check for NULL? > > > > > > As far as I can understand, nand_chip->dev_ready() callback is optional. > > > That's why I decided to use the _optional variant of devm_gpiod_get(). In > > > case of ams-delta, the dev_ready() callback depends on availability of > > > the 'rdy' GPIO pin. As a consequence, I'm checking for both NULL and ERR > > > in order to decide if dev_ready() will be supported. > > > > > > I can pretty well replace it with the standard form and check for ERR only > > > if the purpose of the _optional form is different. > > > > NULL check in practice discards the _optional part of gpiod_get(). So, > > either you use non-optional variant and decide how to handle an > > errors, or user _optional w/o NULL check. > > OK, I'm going to use something like the below while submitting v2: > > - gpiod_rdy = devm_gpiod_get_optional(&pdev->dev, "rdy", GPIOD_IN); > - if (!IS_ERR_OR_NULL(gpiod_rdy)) { > - this->dev_ready = ams_delta_nand_ready; > - } else { > - this->dev_ready = NULL; > - pr_notice("Couldn't request gpio for Delta NAND ready.\n"); > + priv->gpiod_rdy = devm_gpiod_get_optional(&pdev->dev, "rdy", > + GPIOD_IN); > + if (IS_ERR(priv->gpiod_rdy)) { > + err = PTR_ERR(priv->gpiod_nwp); ??? --------------------------------^^^^^^^^^ > + dev_warn(&pdev->dev, "RDY GPIO request failed (%d)\n", err); > + goto err_gpiod; Driver will just use worst case delay instead of RDY signal, so this is perhaps too strict. I will work with degraded performance. ladis > } > > + if (priv->gpiod_rdy) > + this->dev_ready = ams_delta_nand_ready; > > > > > >> > +err_gpiod: > > >> > + if (err = -ENODEV || err = -ENOENT) > > >> > + err = -EPROBE_DEFER; > > >> > > >> Hmm... > > > > > > Amstrad Delta uses gpio-mmio driver. Unfortunatelty that driver is not > > > availble before device init phase, unlike other crucial GPIO drivers which > > > are initialized earlier, e.g. during the postcore or at latetst the > > > subsys phase. Hence, devices which depend on GPIO pins provided by > > > gpio-mmio must either be declared late or fail softly so they get another > > > chance of being probed succesfully. > > > > > > I thought of replacing the gpio-mmio platform driver with bgpio functions > > > it exports but for now I haven't implemented it, not even shared the > > > idea. > > > > > > Does it really hurt to return -EPROBE_DEFER if a GPIO pin can't be > > > obtained? > > I'm only concerned if it would be an infinite defer in the case when > > driver will never appear. > > But I don't remember the details. > > Deferred probes are handled effectively during late_initcall, no risk of > infinite defer, see drivers/base/dd.c for details. > > Thanks, > Janusz > > > > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@alsa-project.org > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel