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

[Julien Grall <julien.grall@xxxxxxx>]

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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