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

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Date:   Sat, 15 Jan 2022 01:09:11 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Liang Yang <liang.yang@...ogic.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 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

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