Hi Andre,
On Mon, 27 Apr 2020 at 12:18, Andre Przywara andre.przywara@arm.com wrote:
Even though the PL011 UART driver claims to be DM compliant, it does not really a good job with parsing DT nodes. U-Boot seems to adhere to a non-standard binding, either requiring to have a "skip-init" property in the node, or to have an extra "clock" property holding the base *frequency* value for the baud rate generator. DTs in the U-Boot tree seem to have been hacked to match this requirement.
One problem is that we want a 'debug UART' to work before the clock driver is running, so we want to do the *minimum possible* amount of init to get the UART running. So we don't want to start up driver model, clock drivers, etc.
I think we should have useful helpers like the 'clock' property to avoid lots of parsing very early in U-Boot. Of course such things are hard for kernel people to understand / agree to but that doesn't make them wrong.
The official binding does not mention any of these properties, instead recommends a standard "clocks" property to point to the baud base clock.
Some boards use simple "fixed-clock" providers, which U-Boot readily supports, so let's add some simple DM clock code to the PL011 driver to learn the rate of the first clock, as described by the official binding.
These clock nodes seem to be not ready very early in the boot process, so provide a fallback value, by re-using the already existing CONFIG_PL011_CLOCK variable.
Signed-off-by: Andre Przywara andre.przywara@arm.com
drivers/serial/serial_pl01x.c | 47 +++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 16 deletions(-)
Reviewed-by: Simon Glass sjg@chromium.org
diff --git a/drivers/serial/serial_pl01x.c b/drivers/serial/serial_pl01x.c index 2a5f256184..14040f32ef 100644 --- a/drivers/serial/serial_pl01x.c +++ b/drivers/serial/serial_pl01x.c @@ -12,6 +12,7 @@
Regards, Simon