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Date:   Thu, 12 Apr 2018 23:11:08 +0800
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Subject: Re: [PATCH 3/5] net: stmmac: dwmac-sun8i: Allow getting syscon regmap from device
To:     Maxime Ripard <maxime.ripard@bootlin.com>
CC:     Rob Herring <robh+dt@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Corentin Labbe <clabbe.montjoie@gmail.com>,
        netdev@vger.kernel.org, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-sunxi@googlegroups.com
From:   Icenowy Zheng <icenowy@aosc.io>
Message-ID: <A027702A-F3F7-4896-B2B8-E024DA521661@aosc.io>
Sender: linux-kernel-owner@vger.kernel.org
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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.

>
>Maxime