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Subject: Re: [linux-sunxi] Re: [PATCH 3/5] net: stmmac: dwmac-sun8i: Allow getting syscon regmap from device
To:     linux-arm-kernel@lists.infradead.org, Chen-Yu Tsai <wens@csie.org>,
        Maxime Ripard <maxime.ripard@bootlin.com>
CC:     devicetree <devicetree@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-sunxi <linux-sunxi@googlegroups.com>,
        Rob Herring <robh+dt@kernel.org>,
        Corentin Labbe <clabbe.montjoie@gmail.com>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
From:   Icenowy Zheng <icenowy@aosc.io>
Message-ID: <B885F825-6131-4F72-A762-17CEB8369893@aosc.io>
Sender: linux-kernel-owner@vger.kernel.org
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于 2018年4月17日 GMT+08:00 下午7:59:38, Chen-Yu Tsai <wens@csie.org> 写到:
>On Tue, Apr 17, 2018 at 7:52 PM, Maxime Ripard
><maxime.ripard@bootlin.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@bootlin.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@aosc.io>
>wrote:
>>> >> > 于 2018年4月12日 GMT+08:00 下午10:56:28, Maxime Ripard
><maxime.ripard@bootlin.com> 写到:
>>> >> >>On Wed, Apr 11, 2018 at 10:16:39PM +0800, Icenowy Zheng wrote:
>>> >> >>> From: Chen-Yu Tsai <wens@csie.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@csie.org>
>>> >> >>> [Icenowy: change to use regmaps with single register, change
>commit
>>> >> >>>  message]
>>> >> >>> Signed-off-by: Icenowy Zheng <icenowy@aosc.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.

In this situation maybe I should send newer revision of A64
drivers to you?

>
>ChenYu
>
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