[PATCH 1/2] ARM: dts: BCM5301X: Specify serial console parameters

On 17-03-14 07:53 AM, Jon Mason wrote:

On Tue, Mar 14, 2017 at 8:32 AM, Rafa? Mi?ecki [off-list ref] wrote:

quoted

On 03/14/2017 01:26 PM, Andrew Lunn wrote:

quoted

On Tue, Mar 14, 2017 at 08:58:29AM +0100, Rafa?? Mi??ecki wrote:

quoted

From: Rafa?? Mi??ecki <rafal@milecki.pl>

This adds baud rate, parity & number of data bits. It's required to get
serial working correctly.

Signed-off-by: Rafa?? Mi??ecki <rafal@milecki.pl>
---
 arch/arm/boot/dts/bcm5301x.dtsi | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/bcm5301x.dtsi

b/arch/arm/boot/dts/bcm5301x.dtsi
index 8fd1ef9f0c2d..468107166a6f 100644

--- a/arch/arm/boot/dts/bcm5301x.dtsi
+++ b/arch/arm/boot/dts/bcm5301x.dtsi

@@ -18,8 +18,12 @@
 / {
        interrupt-parent = <&gic>;

+       aliases {
+               serial0 = &uart0;
+       };
+
        chosen {
-               stdout-path = &uart0;
+               stdout-path = "serial0:115200n8";
        };

Hi Rafal

The alias is fine. But putting the stdout-path here is unusual. Which
serial port is used for console is board specific, where as
bcm5301x.dtsi is very generic, it describes the SoC, not a board.  If
you look at other .dtsi files, those that specify stdout-path contain
properties which are common to a range of similar boards.

So far I've never seen any board using other uart. Also uart0 is disabled by
default and we enable it per board family (BCM4708 / BCM47081 / BCM4709 /
BCM47094). I think it's just more practical to have simple DTS that covers
99,9% boards by default and handled that margin of devices separately.

We already got a lot of duplicated code for enabling uart0, see:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7b790d3b2943bf8e7e7bafe184008bd6451fe0bd

Jon Mason from Broadcom who knows this hardware and designs very well
confirmed
it's a sane/safe assumption.

It should work for all the boards.  The question is whether it should
be in the DTSI or DTS file.  This code replicates code I have in
arch/arm/boot/dts/bcm953012k.dts
So, either it should be removed or we should change all of the other
DTS files to have this entry.  My understanding is that the latter
approach is the acceptable one (which matches Andrew's comment), but I
can make the other changes if necessary.

dtsi file is fine to handle 99% of the use cases and not duplicate the 
entry.  This is what we do for newer SoCs (such as Cygnus) where the 
console will always be a particular UART (as the BootROM already uses a 
certain UART the boards are designed to use that UART as the console 
always).  For bcm953012 a similar situation exists as a common 
bootloader is used across boards.  So, the uart used as the terminal 
will always be the same.

I don't see a good reason for duplicating the code in every dts file.

Acked-by: Scott Branden <scott.branden@broadcom.com>

Thanks,
Jon