linux-kernel - Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG

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Message-ID: <CAMuHMdUEbkp4neqP_p5Srp_nfASd4aTKNqzL7LNRnvFDxWUGCw@mail.gmail.com>
Date:	Thu, 10 Dec 2015 10:21:27 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Simon Horman <horms@...ge.net.au>
Cc:	Geert Uytterhoeven <geert+renesas@...der.be>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/25] serial: sh-sci: Correct SCIF type on R-Car for BRG

On Fri, Nov 20, 2015 at 4:33 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Friday 20 November 2015 16:30:22 Geert Uytterhoeven wrote:
>> On Fri, Nov 20, 2015 at 3:52 PM, Laurent Pinchart wrote:
>> > On Friday 20 November 2015 08:46:56 Geert Uytterhoeven wrote:
>> >> On Thu, Nov 19, 2015 at 9:55 PM, Laurent Pinchart wrote:
>> >>> On Thursday 19 November 2015 19:38:56 Geert Uytterhoeven wrote:
>> >>>> The "renesas,scif" compatible value is currently used for the SCIF
>> >>>> variant in all Renesas SoCs of the R-Car family.  However, the variant
>> >>>> used in the R-Car family is not the common "SH-4(A)" variant, but a
>> >>>> derivative with added "Baud Rate Generator for External Clock" (BRG),
>> >>>> which is also present in sh7734.
>> >>>
>> >>> Time to introduce a "renesas,scif-rcar" compatible string ? ;-)
>> >>>
>> >>> As the only DT-enabled platform to have a different SCIF type is
>> >>> r7s72100 we could also consider just switching the regtype to
>> >>> SCIx_SH4_SCIF_BRG_REGTYPE for the generic "renesas,scif" entry as it's
>> >>> listed after the "renesas,scif- r7s72100" entry. That might cause an
>> >>> issue if we want to enable DT on arch/sh though, but even if that
>> >>> happens due to the J-Core processors I'd be surprised to see the old
>> >>> Renesas SH platforms being moved to DT.
>> >>
>> >> I thought about that, but you never know in which out-of-tree BSP it
>> >> ended up being used, too. So better safe than sorry.
>> >
>> > Out-of-tree should be banned :-)
>> >
>> > More seriously, I suppose you wouldn't be thrilled by the idea of a
>> > "renesas,scif-rcar-gen2" ?
>>
>> Nope. Note that it's also used in R-Car Gen 1 and Gen 3, and sh7734.
>
> Yes, but it would at least cover the whole Gen2 family that behaves the same
> way. And wouldn't preclude adding "renesas,scif-rcar-gen1". That's two compat
> strings only.

In light of all the recent "add fallback compatibility strings" patch series
from Simon, perhaps I should reconsider, and just match against three (new)
family-specific compatible values:

    "renesas,scif-rcar-gen1"
    "renesas,scif-rcar-gen2"
    "renesas,scif-rcar-gen3"

instead of the 8 (and more coming) SoC-specific compatible values?

Following that scheme means we will have to add many compatible values
to the existing dtsis. I.e. every SCIx device node (there are more than 100)
will have 3, like

        scif0: serial@...60000 {
                compatible = "renesas,scif-r8a7791", "renesas,scif-rcar-gen2",
                              "renesas,scif";

Not having the SoC-specific ones in the driver won't cause an issue when using
an old DTS with a new kernel: you can't use the new BRG features without
adding the extra clocks to the DTS anyway, so you can add the family-specific
compatible value when doing that update.

Simon, what do you think?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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