linux-kernel - Re: [linux-sunxi] Re: [PATCH 3/5] net: stmmac: dwmac-sun8i: Allow getting syscon regmap from device

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Message-ID: <CAGb2v66e+tWsYqzpOnRaJtjq4OneUOruszYML0FnvAGbXi5qsw@mail.gmail.com>
Date:   Tue, 17 Apr 2018 19:59:38 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Icenowy Zheng <icenowy@...c.io>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        netdev <netdev@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] Re: [PATCH 3/5] net: stmmac: dwmac-sun8i: Allow
 getting syscon regmap from device

On Tue, Apr 17, 2018 at 7:52 PM, Maxime Ripard
<maxime.ripard@...tlin.com> wrote:
> On Mon, Apr 16, 2018 at 10:51:55PM +0800, Chen-Yu Tsai wrote:
>> On Mon, Apr 16, 2018 at 10:31 PM, Maxime Ripard
>> <maxime.ripard@...tlin.com> wrote:
>> > On Thu, Apr 12, 2018 at 11:23:30PM +0800, Chen-Yu Tsai wrote:
>> >> On Thu, Apr 12, 2018 at 11:11 PM, Icenowy Zheng <icenowy@...c.io> wrote:
>> >> > 于 2018年4月12日 GMT+08:00 下午10:56:28, Maxime Ripard <maxime.ripard@...tlin.com> 写到:
>> >> >>On Wed, Apr 11, 2018 at 10:16:39PM +0800, Icenowy Zheng wrote:
>> >> >>> From: Chen-Yu Tsai <wens@...e.org>
>> >> >>>
>> >> >>> On the Allwinner R40 SoC, the "GMAC clock" register is in the CCU
>> >> >>> address space; on the A64 SoC this register is in the SRAM controller
>> >> >>> address space, and with a different offset.
>> >> >>>
>> >> >>> To access the register from another device and hide the internal
>> >> >>> difference between the device, let it register a regmap named
>> >> >>> "emac-clock". We can then get the device from the phandle, and
>> >> >>> retrieve the regmap with dev_get_regmap(); in this situation the
>> >> >>> regmap_field will be set up to access the only register in the
>> >> >>regmap.
>> >> >>>
>> >> >>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>> >> >>> [Icenowy: change to use regmaps with single register, change commit
>> >> >>>  message]
>> >> >>> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
>> >> >>> ---
>> >> >>>  drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c | 48
>> >> >>++++++++++++++++++++++-
>> >> >>>  1 file changed, 46 insertions(+), 2 deletions(-)
>> >> >>>
>> >> >>> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
>> >> >>b/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
>> >> >>> index 1037f6c78bca..b61210c0d415 100644
>> >> >>> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
>> >> >>> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
>> >> >>> @@ -85,6 +85,13 @@ const struct reg_field old_syscon_reg_field = {
>> >> >>>      .msb = 31,
>> >> >>>  };
>> >> >>>
>> >> >>> +/* Specially exported regmap which contains only EMAC register */
>> >> >>> +const struct reg_field single_reg_field = {
>> >> >>> +    .reg = 0,
>> >> >>> +    .lsb = 0,
>> >> >>> +    .msb = 31,
>> >> >>> +};
>> >> >>> +
>> >> >>
>> >> >>I'm not sure this would be wise. If we ever need some other register
>> >> >>exported through the regmap, will have to change all the calling sites
>> >> >>everywhere in the kernel, which will be a pain and will break
>> >> >>bisectability.
>> >> >
>> >> > In this situation the register can be exported as another
>> >> >  regmap. Currently the code will access a regmap with name
>> >> > "emac-clock" for this register.
>> >> >
>> >> >>
>> >> >>Chen-Yu's (or was it yours?) initial solution with a custom writeable
>> >> >>hook only allowing a single register seemed like a better one.
>> >> >
>> >> > But I remember you mentioned that you want it to hide the
>> >> > difference inside the device.
>> >>
>> >> The idea is that a device can export multiple regmaps. This one,
>> >> the one named "gmac" (in my soon to come v2) or "emac-clock" here,
>> >> is but one of many possible regmaps, and it only exports the register
>> >> needed by the GMAC/EMAC.
>> >
>> > I'm not sure this would be wise either. There's a single register map,
>> > and as far as I know we don't have a binding to express this in the
>> > DT. This means that the customer and provider would have to use the
>> > same name, but without anything actually enforcing it aside from
>> > "someone in the community knows it".
>> >
>> > This is not a really good design, and I was actually preferring your
>> > first option. We shouldn't rely on any undocumented rule. This will be
>> > easy to break and hard to maintain.
>>
>> So, one regmap per device covering the whole register range, and the
>> consumer knows which register to poke by looking at its own compatible.
>>
>> That sound right?
>
> Yep. And ideally, sending a single serie for both the A64 and the R40
> cases, in order to provide the big picture.

OK. I'll incorporate Icenowy's stuff into my series.

ChenYu