From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Date: Mon, 8 Aug 2016 22:28:53 -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> Message-ID: <88a6384e-ddd1-6a5b-4e82-82c565b53036@wwwdotorg.org> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de 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 :).