linux-kernel - Re: [PATCH v9 3/4] clk: meson: add DT documentation for emmc clock controller

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Date:   Mon, 17 Jan 2022 15:03:47 +0800
From:   Liang Yang <liang.yang@...ogic.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     Stephen Boyd <sboyd@...nel.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Rob Herring <robh+dt@...nel.org>, <linux-clk@...r.kernel.org>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Victor Wan <victor.wan@...ogic.com>,
        XianWei Zhao <xianwei.zhao@...ogic.com>,
        Kelvin Zhang <kelvin.zhang@...ogic.com>,
        BiChao Zheng <bichao.zheng@...ogic.com>,
        YongHui Yu <yonghui.yu@...ogic.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 3/4] clk: meson: add DT documentation for emmc clock
 controller

Hi Martin,

On 2022/1/15 8:09, Martin Blumenstingl wrote:
> [ EXTERNAL EMAIL ]
> 
> Hi Liang,
> 
> On Fri, Jan 14, 2022 at 4:06 AM Liang Yang <liang.yang@...ogic.com> wrote:
> [...]
>>>> +properties:
>>>> +  compatible:
>>>> +    enum:
>>>> +      - "amlogic,axg-mmc-clkc", "syscon"
>>>
>>> Why is it a syscon?
>>
>> The register documented by reg is shared with SD/eMMC controller port C,
>> and it need to be ops on NFC driver.
> Can you please share an example how the .dts would look like in the
> end for two example cases:
> 1) using the sd_emmc_c MMC interface > 2) not using the MMC interface of sd_emmc_c but only using it's clocks
> for the NFC
I think both EMMC(although it is not implemented by 'axg-mmc-clkc'  yet) 
and NAND clock have the same way in dts:
		......
		clocks = <&clkc CLKID_SD_EMMC_C>,
			<&sd_emmc_c_clkc CLKID_MMC_DIV>,
			<&sd_emmc_c_clkc CLKID_MMC_PHASE_RX>,
			<&sd_emmc_c_clkc CLKID_MMC_PHASE_TX>;
		clock-names = "core", "device", "rx", "tx";
		amlogic,mmc-syscon = <&sd_emmc_c_clkc>;
		......

> 
> Initially I wanted to suggest the usage of a sub-node with compatible
> = "mmc-slot" (see
> Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.txt for an
> example) to decide whether the MMC controller is registered or whether
> just the clock controller is registered.
> However, the mmc-slot compatible string is not documented in
> Documentation/devicetree/bindings/mmc/mmc-controller.yaml currently.
> Maybe the MMC maintainers have any suggestions if other IPs have
> similar requirements (for IPs with shared parts).
> 
> 
> Best regards,
> Martin
> 
> .