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: <8B16E29B-B5B9-4FCE-91F0-F4B0D909EAE1@aosc.io>
Date:   Mon, 16 Apr 2018 22:34:37 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>
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



于 2018年4月16日 GMT+08:00 下午10:31:30, Maxime Ripard <maxime.ripard@...tlin.com> 写到:
>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.

Okay. Then I will revert back to the original solution in the next version.

>
>Maxime