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

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Date:   Thu, 12 Apr 2018 23:23:30 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        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 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.

Hi,

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. IMHO it is highly unlikely the same piece of
hardware would need a second register from the same device. A more
likely situation would be it needs another register from a different
device, like on the H6 where the "internal PHY" is not so internal
from a system bus point of view.

ChenYu