linux-kernel - Re: [PATCH v5 1/2] spi: Add Renesas R-Car Gen3 RPC-IF SPI controller driver

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Date:   Thu, 17 Jan 2019 09:19:10 +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 v5 1/2] spi: Add Renesas R-Car Gen3 RPC-IF SPI controller driver

Hi Mason,

On Thu, Jan 17, 2019 at 7:32 AM <masonccyang@...c.com.tw> wrote:
> > "Sergei Shtylyov" <sergei.shtylyov@...entembedded.com>
> > 2019/01/17 上午 03:36
> > >>
> > >> [...]
> > >> > +#define RPC_WBUF      0x8000   // Write Buffer
> > >> > +#define RPC_WBUF_SIZE      256   // Write Buffer size
> > >>
> > >>    I wonder if the write buffer should be in a separate "reg" prop tuple...
> > >> Have you considered that?
> > >>
> > >
> > > I don't get your point!
> >
> >    I mean that the write buffer should be a separate "reg" property
> > address/size tuple,
> > so that the RPC device has 3 memory resources. Our SPI driver used
> > this scheme, and I
> > like it.
> >
>
> I got your point but I think this RPC_WBUF@...E20_8000 is in the same group
> and it's size only 256 bytes, not like external address space read mode
> @0x0800_0000 w/ 64K bytes.
>
> Maybe Geert or Marek could comment on it, thanks.

Given the writer buffer is separate from the other registers (it's in
a different
4 KiB page, and thus may be at a different offset on future SoCs), and not
present on RZ/A1, I think it's a good idea to use a separate reg entry for it.

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