linux-kernel - Re: [PATCH v7 1/2] spi: Add Renesas R-Car Gen3 RPC-IF SPI controller driver

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Date:   Thu, 24 Jan 2019 10:12:54 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Mason Yang <masonccyang@...c.com.tw>
Cc:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Simon Horman <horms@...ge.net.au>, juliensu@...c.com.tw,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>, zhengxunli@...c.com.tw
Subject: Re: [PATCH v7 1/2] spi: Add Renesas R-Car Gen3 RPC-IF SPI controller driver

Hi Mason,

On Thu, Jan 24, 2019 at 3:07 AM <masonccyang@...c.com.tw> wrote:
> > "Sergei Shtylyov" <sergei.shtylyov@...entembedded.com>
> > 2019/01/24 上午 02:04

> > > +static const struct of_device_id rpc_spi_of_ids[] = {
> > > +   { .compatible = "renesas,r8a77995-rpc", },
> >
> >    Why (if it has no differences with the generic gen3 value below)?
> > Please remove.
>
> By Geert's comments in dts,
>
>          rpc: rpc@...00000 {
>                 compatible = "renesas,r8a7795-rpc", "renesas,rcar-gen3-rpc";
>                 reg = <0 0xee200000 0 0x200>, <0 0x08000000 0 0x4000000>,
>                       <0 0xee208000 0 0x100>;
>
> I modified it to "renesas,r8a77995-rpc" because this is Soc I developed and validated.

There's a difference between compatible values in DT and in drivers:
  - DT should list all compatible values that are applicable, from
    most-specific to least-specific,
  - Drivers should match against the least-specific compatible value that
    is sufficient to get the job done.
    In this case, that's "renesas,rcar-gen3-rpc".

The driver will probably have to be extended to match against
"renesas,r8a77970-rpc" when R-Car V3M support is added, as RPC on V3M
has an extra register that must be set, and thus cannot be declared
compatible with "renesas,rcar-gen3-rpc".

I hope this explanation makes it clearer.

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