From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Glass Date: Fri, 12 Aug 2016 11:21:17 -0600 Subject: [U-Boot] [PATCH v2] serial: bcm283x_mu: Detect disabled serial device In-Reply-To: References: <1470294682-159882-1-git-send-email-agraf@suse.de> <88a6384e-ddd1-6a5b-4e82-82c565b53036@wwwdotorg.org> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi Alex, On 11 August 2016 at 23:27, Alexander Graf wrote: > > >> Am 12.08.2016 um 00:38 schrieb Simon Glass : >> >> Hi Alex, >> >>> On 11 August 2016 at 05:33, Alexander Graf wrote: >>> >>> >>>> On 09.08.16 06:28, Stephen Warren wrote: >>>>> On 08/04/2016 05:15 PM, Alexander Graf wrote: >>>>> >>>>>> On 04 Aug 2016, at 20:11, Stephen Warren wrote: >>>>>> >>>>>> On 08/04/2016 01:11 AM, Alexander Graf wrote: >>>>>>> On the raspberry pi, you can disable the serial port to gain dynamic >>>>>>> frequency >>>>>>> scaling which can get handy at times. >>>>>>> >>>>>>> However, in such a configuration the serial controller gets its rx >>>>>>> queue filled >>>>>>> up with zero bytes which then happily get transmitted on to whoever >>>>>>> calls >>>>>>> getc() today. >>>>>>> >>>>>>> This patch adds detection logic for that case by checking whether >>>>>>> the RX pin is >>>>>>> mapped to GPIO15 and disables the mini uart if it is not mapped >>>>>>> properly. >>>>>>> >>>>>>> That way we can leave the driver enabled in the tree and can >>>>>>> determine during >>>>>>> runtime whether serial is usable or not, having a single binary that >>>>>>> allows for >>>>>>> uart and non-uart operation. >>>>>> >>>>>>> diff --git a/drivers/serial/serial_bcm283x_mu.c >>>>>>> b/drivers/serial/serial_bcm283x_mu.c >>>>>> >>>>>>> @@ -72,9 +87,18 @@ static int bcm283x_mu_serial_probe(struct udevice >>>>>>> *dev) >>>>>>> { >>>>>>> struct bcm283x_mu_serial_platdata *plat = dev_get_platdata(dev); >>>>>>> struct bcm283x_mu_priv *priv = dev_get_priv(dev); >>>>>>> + struct bcm283x_gpio_regs *gpio = (struct bcm283x_gpio_regs >>>>>>> *)plat->gpio; >>>>>>> >>>>>>> priv->regs = (struct bcm283x_mu_regs *)plat->base; >>>>>>> >>>>>>> + /* >>>>>>> + * The RPi3 disables the mini uart by default. The easiest way >>>>>>> to find >>>>>>> + * out whether it is available is to check if the pin is muxed. >>>>>>> + */ >>>>>>> + if (((readl(&gpio->gpfsel1) >> BCM283X_GPIO_GPFSEL1_F15_SHIFT) & >>>>>>> + BCM283X_GPIO_ALTFUNC_MASK) != BCM283X_GPIO_ALTFUNC_5) >>>>>>> + priv->disabled = true; >>>>>>> + >>>>>>> return 0; >>>>>> >>>>>> Comment on the current implementation: Can't probe() return an error >>>>>> if the device should be disabled? That would avoid the need to check >>>>>> priv->disabled in all the other functions. >>>>> >>>>> I guess I should?ve put that in a comment somewhere. Unfortunately we >>>>> can?t. If I just return an error on probe, U-Boot will panic because >>>>> we tell it in a CONFIG define that we require a serial port (grep for >>>>> CONFIG_REQUIRE_SERIAL_CONSOLE). >>>>> >>>>> We could maybe try to unset that define instead? >>>> >>>> Yes, assuming that U-Boot runs just fine with HDMI console only, I think >>>> it's fine to unset CONFIG_REQUIRE_SERIAL_CONSOLE. >>>> >>>>>> Overall comment: I'd rather not put this logic into the UART driver >>>>>> itself; it is system-specific rather than device-specific. I'd also >>>>>> rather not have the UART driver touching GPIO registers; that's not >>>>>> very modular, and could cause problems if the Pi is converted to use >>>>>> DT to instantiate devices. >>>>>> >>>>>> Instead, can we put the logic into board/raspberrypi/rpi/rpi.c? I.e. >>>>>> have some early function come along and enable/disable the >>>>>> bcm2837_serials device object as appropriate? That way it isolates >>>>>> the code to the Pi specifically, and not any other bcm283x board. >>>>>> We'd want to wrap that code in #ifdef CONFIG_PL01X_SERIAL. >>>>> >>>>> We can do that if we can fail at probe time. If we absolutely must >>>>> have a serial driver to work in the first place, that doesn?t work. I >>>>> can try to poke at it, but it?ll be a few days I think :). >>> >>> So I couldn't find a sane way to fail probing based on something defined >>> in the board file, reusing the existing gpio device. >> >> Would it be possible to move this code into the serial driver? > > You mean like in v2 which Stephen nacked? :) Yes :-( Well you can put what you like in the board code, and if this is only on the rpi, then it makes sense. Really though, this is a pinctrl thing, so if there were a pinctrl driver you could just use it. The GPIO driver should not deal with pin muxing. > >> >>> >>> However, there's an easy alternative. We can make the console code just >>> ignore our serial device if we set its pointer to NULL. That way we >>> still have the device, but can contain all logic to disable usage of the >>> mini uart to the board file. >> >> I'm not very keen on that - feels like a hack. What is stopping >> Stephen's idea from working? I could perhaps help with dm plumbing is >> that is the issue... > > The problem is that we need the gpio device to determine whether the pin is muxed. There is no temporal control that I could see that would allow me to be in a place where the gpio device exists, the serial device does not exist, and where I could then not spawn the serial device based on board logic. Can you use board_early_init_f() ? Regards, Simon