Re: [PATCH 6/6] dt-bindings: spi: Document Renesas SPIBSC bindings

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Chris Brandt <Chris.Brandt@renesas.com>
Cc: Mark Brown <broonie@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	Mason Yang <masonccyang@mxic.com.tw>,
	Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Subject: Re: [PATCH 6/6] dt-bindings: spi: Document Renesas SPIBSC bindings
Date: Wed, 4 Dec 2019 09:43:34 +0100	[thread overview]
Message-ID: <CAMuHMdXKSWeBdCDc6u5KWE67nD_9FStr9A_vb_5K=qpQ_y8bSw@mail.gmail.com> (raw)
In-Reply-To: <TY1PR01MB15622365FCCC3C1CB052FD0E8A420@TY1PR01MB1562.jpnprd01.prod.outlook.com>

Hi Chris,

On Tue, Dec 3, 2019 at 11:33 PM Chris Brandt <Chris.Brandt@renesas.com> wrote:
> On Tue, Dec 3, 2019, Geert Uytterhoeven wrote:
> > > +++ b/Documentation/devicetree/bindings/spi/spi-renesas-spibsc.txt
> > > +Required properties:
> > > +- compatible: should be an SoC-specific compatible value, followed by
> > > +               "renesas,spibsc" as a fallback.
> > > +               supported SoC-specific values are:
> > > +               "renesas,r7s72100-spibsc"       (RZ/A1)
> > > +               "renesas,r7s9210-spibsc"        (RZ/A2)
> >
> > Is the fallback valid for RZ/A1, which has its own special match entry in the
> > driver?
> > Will it be valid for R-Car Gen3?
> > If not, you may want to drop it completely.
>
> The fallback would still work for RZ/A1, you just would not be able to
> set the baud rate. But, I have no problem dropping the fallback. I'm fine
> with having a compatible string for each SoC that is known to work for.
>
> I have not tried it with Gen3, but I would guess there will be some minor
> difference that will needed to be accounted for.

OK.

> > > +- reg: should contain three register areas:
> > > +       first for the base address of SPIBSC registers,
> > > +       second for the direct mapping read mode
> > > +- clocks: should contain the clock phandle/specifier pair for the module
> > clock.
> > > +- power-domains: should contain the power domain phandle/specifier pair.
> > > +- #address-cells: should be 1
> > > +- #size-cells: should be 0
> > > +- flash: should be represented by a subnode of the SPIBSC node,
> > > +        its "compatible" property contains "jedec,spi-nor" if SPI is used.
> >
> > What about the "mtd-rom" use for e.g. XIP?
>
> But "mtd-rom" doesn't really have anything to do with the functionality of the
> driver when it is being used in "SPI mode".

Correct. But DT describes hardware.  If the FLASH is used in direct mapped
mode, that should be described in DT.

> Maybe I just remove any mention of this for now.
>
> > interrupts? RZ/A2M seems to have an SPIBSC interrupt, RZ/A1 hasn't.
>
> There was never any interrupts in the SPIBSC.
> But it looks like when they added HyperFlash and OctaFlash support, they put
> in some interrupts for that.
> And now that I look at it, they are for pins labeled RPC_INT, RPC_WC, RPC_RESET.
> (I just realized that "RPC" stands for "Reduced Pin Count")
>
> So....am I supposed to add in that interrupt even though I'm not planning on using
> it??

DT describes hardware, not driver limitations.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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