@@ -1247,6 +1247,31 @@ blsp_uart1_sleep: blsp-uart1-sleep-state {
bias-pull-down;
};
+ blsp_uart1_console_default: blsp-uart1-console-default-state {
+ tx-pins {
+ pins = "gpio0";
+ function = "blsp_uart1";
+ drive-strength = <16>;
+ bias-disable;
+ bootph-all;
+ };
+
+ rx-pins {
+ pins = "gpio1";
+ function = "blsp_uart1";
+ drive-strength = <16>;
+ bias-pull-up;
+ bootph-all;
+ };
+ };
+
+ blsp_uart1_console_sleep: blsp-uart1-console-sleep-state {
+ pins = "gpio0", "gpio1";
+ function = "gpio";
+ drive-strength = <2>;
+ bias-pull-down;
+ };
+
blsp_uart2_default: blsp-uart2-default-state {
pins = "gpio4", "gpio5";
function = "blsp_uart2";
@@ -1254,7 +1279,25 @@ blsp_uart2_default: blsp-uart2-default-state {
bias-disable;
};
- blsp_uart2_sleep: blsp-uart2-sleep-state {
+ blsp_uart2_console_default: blsp-uart2-console-default-state {
+ tx-pins {
+ pins = "gpio4";
+ function = "blsp_uart2";
+ drive-strength = <16>;
+ bias-disable;
+ bootph-all;
+ };
+
+ rx-pins {
+ pins = "gpio5";
+ function = "blsp_uart2";
+ drive-strength = <16>;
+ bias-pull-up;
+ bootph-all;
+ };
+ };
+
+ blsp_uart2_sleep: blsp_uart2_console_sleep: blsp-uart2-sleep-state {
pins = "gpio4", "gpio5";
function = "gpio";
drive-strength = <2>;
@@ -919,6 +919,31 @@ blsp_uart1_sleep: blsp-uart1-sleep-state {
bias-pull-down;
};
+ blsp_uart1_console_default: blsp-uart1-console-default-state {
+ tx-pins {
+ pins = "gpio0";
+ function = "blsp_uart1";
+ drive-strength = <16>;
+ bias-disable;
+ bootph-all;
+ };
+
+ rx-pins {
+ pins = "gpio1";
+ function = "blsp_uart1";
+ drive-strength = <16>;
+ bias-pull-up;
+ bootph-all;
+ };
+ };
+
+ blsp_uart1_console_sleep: blsp-uart1-console-sleep-state {
+ pins = "gpio0", "gpio1";
+ function = "gpio";
+ drive-strength = <2>;
+ bias-pull-down;
+ };
+
blsp_uart2_default: blsp-uart2-default-state {
pins = "gpio4", "gpio5";
function = "blsp_uart2";
@@ -926,7 +951,25 @@ blsp_uart2_default: blsp-uart2-default-state {
bias-disable;
};
- blsp_uart2_sleep: blsp-uart2-sleep-state {
+ blsp_uart2_console_default: blsp-uart2-console-default-state {
+ tx-pins {
+ pins = "gpio4";
+ function = "blsp_uart2";
+ drive-strength = <16>;
+ bias-disable;
+ bootph-all;
+ };
+
+ rx-pins {
+ pins = "gpio5";
+ function = "blsp_uart2";
+ drive-strength = <16>;
+ bias-pull-up;
+ bootph-all;
+ };
+ };
+
+ blsp_uart2_sleep: blsp_uart2_console_sleep: blsp-uart2-sleep-state {
pins = "gpio4", "gpio5";
function = "gpio";
drive-strength = <2>;
At the moment, msm8916/39.dtsi have two inconsistent UART pinctrl templates that are used by all the boards: - &blsp_uart1_default configures all 4 pins (TX, RX, CTS, RTS), some boards then limit this to just RX and TX - &blsp_uart2_default only configures 2 pins (TX, RX), even though UART2 also supports CTS/RTS It's difficult to define a generic pinctrl template for all UART use cases, since they are quite different in practice. The main use case for most of the 40+ MSM8916/39-based boards upstream is the UART debug console. The current generic template is lacking some properties to work properly: - bias-pull-up for RX: Generally, UART is push-pull and does not need pull up/down. Both sides drive TX, so RX should never be floating. This is why the current pinctrl in msm8916/39.dtsi uses bias-disable. However, this assumes that UART is always connected. For the debug console this will be rarely the case on mobile devices, only during debugging sessions. The rest of the time, the RX pin is floating. This has never caused massive problems, but it's obvious now that this needs fixing: (1) In U-Boot, we have been fighting with problems with autoboot for years. Most of the time, there is a single \0 byte ("break event") read during boot, which interrupts the autoboot process. I tried to work around that by inserting some random delay [1], but it turned out this is also not working reliably on all boards. What happens is: Since RX is floating, it switches randomly between high or low. A long low state is interpreted as "break event" (\0). (2) In postmarketOS, we used to have the "magic SysRq key" enabled by default for the serial console. We had to disable this at some point, because there was a small number of users who were reporting sysrq spam in the kernel log, possibly even crashes/panics triggered by sysrq. What likely happened is: SysRq is triggered by sending a "break event", like in (1). With enough luck, you could even trigger any of the SysRq actions if the RX pin switches between high and low (e.g. because of noise introduced by the LTE radio close by). We can fix this using bias-pull-up, but this may be unneeded, unexpected, or even unwanted for other UART use cases. - bootph-all: U-Boot needs to know which pinctrl to apply during early boot stages, so we should specify "bootph-all" for the console UART pinctrl. Without bootph-all, the bias-pull-up won't be applied early enough in U-Boot to avoid the problem with autoboot in point (1) above. It doesn't make sense to specify this for the other UART instances. bootph-all is a generic property documented in dt-schema bootph.yaml. Define these two additional properties only for the debug UART console, by defining a new pinctrl template specifically for that. In the following commits, boards will be converted to use these where appropriate. [1]: https://source.denx.de/u-boot/u-boot/-/commit/ad7e967738a9c639e07cf50b83ffccdf9a8537b0 Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com> Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org> --- arch/arm64/boot/dts/qcom/msm8916.dtsi | 45 ++++++++++++++++++++++++++++++++++- arch/arm64/boot/dts/qcom/msm8939.dtsi | 45 ++++++++++++++++++++++++++++++++++- 2 files changed, 88 insertions(+), 2 deletions(-)