On Wed, Jul 10, 2024 at 7:29 AM André Draszik <andre.draszik@xxxxxxxxxx> wrote: > > While gs101 needs exactly two clocks for the UART, the schema doesn't > currently limit the maximum number to this and instead the default of > five from this schema is applied. > > Update the schema accordingly. > > Also, as pointed out in [1] before, the hand-over between earlycon and > serial console is fragile due to clocking issues, at least on Google > Tensor gs101. Therefore, document the clocking requirements for > earlycon in the description for posterity, so the information is not > lost. > > Link: https://lore.kernel.org/all/d45de3b2bb6b48653842cf1f74e58889ed6783ae.camel@xxxxxxxxxx/ [1] > Signed-off-by: André Draszik <andre.draszik@xxxxxxxxxx> > --- > Documentation/devicetree/bindings/serial/samsung_uart.yaml | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/Documentation/devicetree/bindings/serial/samsung_uart.yaml b/Documentation/devicetree/bindings/serial/samsung_uart.yaml > index 0f0131026911..2435c3d92158 100644 > --- a/Documentation/devicetree/bindings/serial/samsung_uart.yaml > +++ b/Documentation/devicetree/bindings/serial/samsung_uart.yaml > @@ -145,6 +145,20 @@ allOf: > - samsung,uart-fifosize > properties: > reg-io-width: false blank line between properties > + clocks: > + description: | > + Note that for earlycon to work, the respective ipclk and pclk need > + to be running! The bootloader normally leaves them enabled, but the > + serial driver will start handling those clocks before the console > + driver takes over from earlycon, breaking earlycon. If earlycon is > + required, please revert the patch "clk: samsung: gs101: don't mark > + non-essential (UART) clocks critical" locally first to mark them > + CLK_IS_CRITICAL and avoid this problem. That's a whole bunch of details that are Linux specific which have little to do with the binding. > + maxItems: 2 > + clock-names: > + items: > + - const: uart > + - const: clk_uart_baud0 Which clock is pclk and ipclk? 'baud' would be sufficient for the name. 'clk_' and 'uart' are redundant because it's all clocks and they are all for the uart. Rob
