From: Harald Geyer <harald@ccbib.org> To: Maxime Ripard <maxime.ripard@bootlin.com> Cc: Mark Rutland <mark.rutland@arm.com>, devicetree@vger.kernel.org, info@olimex.com, Mark Brown <broonie@kernel.org>, Chen-Yu Tsai <wens@csie.org>, Rob Herring <robh+dt@kernel.org>, Torsten Duwe <duwe@lst.de>, ibu@radempa.de, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH RFC] arm64: dts: allwinner: a64: teres-i: Enable audio Date: Wed, 13 Feb 2019 12:43:46 +0100 Message-ID: <E1gtsx9-0000RP-08@stardust.g4.wien.funkfeuer.at> (raw) In-Reply-To: <20190213094442.da2dy6d5bb527nft@flea> Hi Maxime! Maxime Ripard writes: > On Tue, Feb 12, 2019 at 08:37:36PM +0100, Harald Geyer wrote: > > > There's a few issues with that approach as well: > > > > > > - We're actively trying to remove the pinctrl nodes for the GPIOs > > > > For what reason? Maybe it doesn't apply to this usecase? > > This is kind of separate. At the moment, on all our SoCs but the H6, > requesting a pin to a separate state using pinctrl doesn't mark the > GPIO muxed on that pin as reserved, so through the GPIO userspace > interface (or calling gpio_request from within the kernel, but that > seems less of a risk) anyone is free to just request a GPIO on a pin > already requested, behind the consumer drivers' back. Which is pretty > bad. Really, I'm surprised. This is not the behaviour I remember from A20 and A64. Indeed, testing this on teres with the debug detect pin claimed by audio, I get: root@teres:/sys/kernel/debug/pinctrl/1f02c00.pinctrl# cat pinmux-pins Pinmux settings per pin Format: pin (name): mux_owner|gpio_owner (strict) hog? pin 352 (PL0): device 1f03400.rsb function s_rsb group PL0 pin 353 (PL1): device 1f03400.rsb function s_rsb group PL1 pin 354 (PL2): GPIO 1f02c00.pinctrl:354 pin 355 (PL3): UNCLAIMED pin 356 (PL4): UNCLAIMED pin 357 (PL5): UNCLAIMED pin 358 (PL6): UNCLAIMED pin 359 (PL7): GPIO 1f02c00.pinctrl:359 pin 360 (PL8): GPIO 1f02c00.pinctrl:360 pin 361 (PL9): device sound function gpio_out group PL9 pin 362 (PL10): UNCLAIMED pin 363 (PL11): UNCLAIMED pin 364 (PL12): GPIO 1f02c00.pinctrl:364 [...] root@teres:/sys/class/gpio# echo 361 >export bash: echo: Schreibfehler: Das Argument ist ungültig. So I can't access this from sysfs, even though the error code is a bit odd: I'd expect EBUSY instead of EINVAL. I can export any of the UNCLAIMED pins/gpios. Trying with libgpiod as well, I see that the state of the pin is reported incorretly, but I still can't access it: gpiochip0 - 32 lines: line 0: unnamed unused input active-high line 1: unnamed unused input active-high line 2: unnamed "reset" output active-low [used] line 3: unnamed unused input active-high line 4: unnamed unused input active-high line 5: unnamed unused input active-high line 6: unnamed unused input active-high line 7: unnamed "usb1-vbus" output active-high [used] line 8: unnamed "Lid Switch" input active-low [used] line 9: unnamed unused input active-high line 10: unnamed "sysfs" input active-high [used] line 11: unnamed unused input active-high line 12: unnamed "enable" output active-high [used] line 13: unnamed unused input active-high root@teres:~# gpioget 1f02c00.pinctrl 9 gpioget: error reading GPIO values: Invalid argument On a pin exported to sysfs I get EBUSY as expected: root@teres:~# gpioget 1f02c00.pinctrl 10 gpioget: error reading GPIO values: Device or resource busy And reading an unclaimed pin works as expected too: root@teres:~# gpioget 1f02c00.pinctrl 11 0 Either I misunderstood what you have written or it isn't true. > There's support for such a check in pinctrl, and we did enable it for > the H6. However, one of its side effect is that you can't have a > pinctrl node for a GPIO anymore (at least without significantly > reworking the GPIO API in the kernel). Can you point me to some background reading? > We did enable it for the H6, since it didn't have any backward > compatibility to take care of, but it's disabled at the moment for all > the other SoCs to be able to flip that switch at some point. And > that's why we're moving away from it as well. Well ... that's good to know, because I have a couple of custom DTs with pinctrl nodes for a GPIO. I think it should be documented as deprecated in the binding then. Also I wonder how I can select drive strength or bias on a gpio line when I can't use pinctrl with them anymore. > > I think the real downside of this approach is, that using the UART > > makes the internal speakers/mic unuseable too. > > That's also a pretty big issue. I certainly agree it's unfortunate. > > But we need a way to control the mux from userspace and aside from > > unbinding the ideas proposed thus far are: > > > > a) control the gpio directly > > b) control the gpio via leds-gpio > > > > (a) was dismissed because we can't set a default from DT > > (b) was dismissed because some rogue app might try to blink it > > > > The clean solution might be to write mux-gpio, which is actually > > identical to leds-gpio but lives in /sys/class/mux_switches/ and > > uses different filenames. But that's going down the "invent a new > > subsystem road", which I believe is overkill for what is a debugging > > facility for a single board. > > I still believe we should aim at supporting this through pinctrl, and > adding an userspace API is definitely easier than a full subsystem. Getting everybody to agree on a new API (especially a userspace ABI) is a major headache (and rightly so, we want to get something right on the first attempt that is going to stay around forever). I don't think some quirky debugging feature is worth the effort. And frankly I don't care much about audio on the teres. I started working on this because I feel kind of responsible for keeping the teres DT up-to-date with what the kernel can support. But if the kernel can't support it ATM: so be it. As a compromise I think we could add all the nodes to the DT but mark their status as "disabled". That would help everybody wanting to enable audio but still be technically correct. Harald -- If you want to support my work: see http://friends.ccbib.org/harald/supporting/ or donate via CLAM to xASPBtezLNqj4cUe8MT5nZjthRSEjrRQXN or via peercoin to P98LRdhit3gZbHDBe7ta5jtXrMJUms4p7w _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply index Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20190211111245.GA18147@lst.de> 2019-02-11 13:36 ` Harald Geyer 2019-02-11 15:39 ` Maxime Ripard 2019-02-11 19:32 ` Harald Geyer 2019-02-12 8:38 ` Maxime Ripard 2019-02-12 9:42 ` Harald Geyer 2019-02-12 10:09 ` Maxime Ripard 2019-02-12 19:37 ` Harald Geyer 2019-02-13 9:44 ` Maxime Ripard 2019-02-13 11:43 ` Harald Geyer [this message] 2019-02-13 15:53 ` Maxime Ripard 2019-02-14 0:12 ` Harald Geyer 2019-02-15 14:20 ` Torsten Duwe 2019-02-16 20:47 ` Harald Geyer 2019-02-17 11:30 ` Torsten Duwe 2019-02-18 10:24 ` Maxime Ripard 2019-04-30 13:32 ` Torsten Duwe 2019-05-02 7:46 ` Maxime Ripard 2019-05-02 14:48 ` Harald Geyer 2019-02-01 11:37 Harald Geyer 2019-02-12 8:34 ` Chen-Yu Tsai
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