netdev - Re: [PATCH net-next 02/12] clk: sunxi-ng: r40: export a regmap to access the GMAC register

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Date:   Tue, 03 Apr 2018 17:52:50 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>
CC:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>
Subject: Re: [PATCH net-next 02/12] clk: sunxi-ng: r40: export a regmap to access the GMAC register



于 2018年4月3日 GMT+08:00 下午5:50:05, Maxime Ripard <maxime.ripard@...tlin.com> 写到:
>On Tue, Apr 03, 2018 at 11:48:45AM +0200, Maxime Ripard wrote:
>> On Tue, Mar 20, 2018 at 03:15:02PM +0800, Chen-Yu Tsai wrote:
>> > On Mon, Mar 19, 2018 at 5:31 AM, Maxime Ripard
>> > <maxime.ripard@...tlin.com> wrote:
>> > > On Sat, Mar 17, 2018 at 05:28:47PM +0800, Chen-Yu Tsai wrote:
>> > >> From: Icenowy Zheng <icenowy@...c.io>
>> > >>
>> > >> There's a GMAC configuration register, which exists on
>A64/A83T/H3/H5 in
>> > >> the syscon part, in the CCU of R40 SoC.
>> > >>
>> > >> Export a regmap of the CCU.
>> > >>
>> > >> Read access is not restricted to all registers, but only the
>GMAC
>> > >> register is allowed to be written.
>> > >>
>> > >> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
>> > >> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>> > >
>> > > Gah, this is crazy. I'm really starting to regret letting that
>syscon
>> > > in in the first place...
>> > 
>> > IMHO syscon is really a better fit. It's part of the glue layer and
>> > most other dwmac user platforms treat it as such and use a syscon.
>> > Plus the controls encompass delays (phase), inverters (polarity),
>> > and even signal routing. It's not really just a group of clock
>controls,
>> > like what we poorly modeled for A20/A31. I think that was really a
>> > mistake.
>> > 
>> > As I mentioned in the cover letter, a slightly saner approach would
>> > be to let drivers add custom syscon entries, which would then
>require
>> > less custom plumbing.
>> 
>> A syscon is convenient, sure, but it also bypasses any abstraction
>> layer we have everywhere else, which means that we'll have to
>maintain
>> the register layout in each and every driver that uses it.
>> 
>> So far, it's only be the GMAC, but it can also be others (the SRAM
>> controller comes to my mind), and then, if there's any difference in
>> the design in a future SoC, we'll have to maintain that in the GMAC
>> driver as well.
>
>I guess I forgot to say something, I'm fine with using a syscon we
>already have.
>
>I'm just questionning if merging any other driver using one is the
>right move.

Even for current SoCs supported by dwnac-sun8i, there
is a syscon/sram-controller problem. They're both at 0x1c00000.

The first examples for the need of sram-controller is
A64, which we need to claim SRAM C for DE2 access.

>
>Maxime