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Re: [Xen-devel] [PATCH v1 3/4] xen/arm: Add SCIFA UART support for early printk





On 07/08/18 15:28, Oleksandr Tyshchenko wrote:
On Tue, Aug 7, 2018 at 4:48 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
Hi,

Hi, Julien


On 06/08/18 19:35, Oleksandr Tyshchenko wrote:

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Add support for Renesas "Stout" development board based on
R-Car H2 SoC which has SCIFA compatible UART.

Actually existing SCIF UART support (debug-scif.inc) and
newly added SCIFA UART support (debug-scifa.inc) differ only
in registers offsets.

In that case, could we just extend debug-scif.inc?
I was thinking about that, but couldn't find suitable solution without
adding extra config option.

I had the config option in my mind. But it may not be worth it.

As I understand, we need to recognize in run-time somehow which
interface is present to use proper register offsets,
so in UART driver it is easy to recognize using device-tree compatible
string, but what to do here in such an early code.



Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
---
   docs/misc/arm/early-printk.txt     |  3 ++-
   xen/arch/arm/Rules.mk              |  1 +
   xen/arch/arm/arm32/debug-scifa.inc | 51
++++++++++++++++++++++++++++++++++++++
   3 files changed, 54 insertions(+), 1 deletion(-)
   create mode 100644 xen/arch/arm/arm32/debug-scifa.inc

diff --git a/docs/misc/arm/early-printk.txt
b/docs/misc/arm/early-printk.txt
index f765f59..f1b55d3 100644
--- a/docs/misc/arm/early-printk.txt
+++ b/docs/misc/arm/early-printk.txt
@@ -39,12 +39,13 @@ the name of the machine:
     - fastmodel: printk on ARM Fastmodel software emulators
     - hikey960: printk with pl011 with Hikey 960
     - juno: printk with pl011 on Juno platform
-  - lager: printk with SCIF0 on Renesas R-Car H2 processors
+  - lager: printk with SCIF0 on Renesas Lager board (R-Car H2 processor)


Why this change?
This sentence was not entirely correct. Since SCIF0 interface is
applicable for Lager
board, but is not applicable for Stout board which also based on R-Car
H2 processor.
Shall I create a separate patch for this small correction?

Yes please.



     - midway: printk with the pl011 on Calxeda Midway processors
     - mvebu: printk with the MVEBU for Marvell Armada 3700 SoCs
     - omap5432: printk with UART3 on TI OMAP5432 processors
     - rcar3: printk with SCIF2 on Renesas R-Car Gen3 processors
     - seattle: printk with pl011 for AMD Seattle processor
+  - stout: printk with SCIFA0 on Renesas Stout board (R-Car H2 processor)


I have started to look at porting that to Kconfig ealyprintk and it is a
massive pain. So I would tend to prefer if we avoid adding more convenience
alias and instead document on the wiki page how to use earlyprintk for that.
I will update a wiki page. Shall I drop this string in early-printk.txt?

Yes please.

Cheers,

--
Julien Grall

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