From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Date: Fri, 12 Aug 2016 07:27:38 +0200 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 > 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? :) > >> >> 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. Alex