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    SubjectRe: [PATCH v1 2/2] arm: dts: mt2701: add nor flash node
    On Fri, 13 Jan 2017 17:13:55 +0100
    Marek Vasut <marek.vasut@gmail.com> wrote:

    > On 01/13/2017 04:12 PM, Matthias Brugger wrote:
    > >
    > >
    > > On 13/01/17 15:17, Boris Brezillon wrote:
    > >> On Fri, 13 Jan 2017 15:13:29 +0800
    > >> Guochun Mao <guochun.mao@mediatek.com> wrote:
    > >>
    > >>> Add Mediatek nor flash node.
    > >>>
    > >>> Signed-off-by: Guochun Mao <guochun.mao@mediatek.com>
    > >>> ---
    > >>> arch/arm/boot/dts/mt2701-evb.dts | 25 +++++++++++++++++++++++++
    > >>> arch/arm/boot/dts/mt2701.dtsi | 12 ++++++++++++
    > >>> 2 files changed, 37 insertions(+)
    > >>>
    > >>> diff --git a/arch/arm/boot/dts/mt2701-evb.dts
    > >>> b/arch/arm/boot/dts/mt2701-evb.dts
    > >>> index 082ca88..85e5ae8 100644
    > >>> --- a/arch/arm/boot/dts/mt2701-evb.dts
    > >>> +++ b/arch/arm/boot/dts/mt2701-evb.dts
    > >>> @@ -24,6 +24,31 @@
    > >>> };
    > >>> };
    > >>>
    > >>> +&nor_flash {
    > >>> + pinctrl-names = "default";
    > >>> + pinctrl-0 = <&nor_pins_default>;
    > >>> + status = "okay";
    > >>> + flash@0 {
    > >>> + compatible = "jedec,spi-nor";
    > >>> + reg = <0>;
    > >>> + };
    > >>> +};
    > >>> +
    > >>> +&pio {
    > >>> + nor_pins_default: nor {
    > >>> + pins1 {
    > >>> + pinmux = <MT2701_PIN_240_EXT_XCS__FUNC_EXT_XCS>,
    > >>> + <MT2701_PIN_241_EXT_SCK__FUNC_EXT_SCK>,
    > >>> + <MT2701_PIN_239_EXT_SDIO0__FUNC_EXT_SDIO0>,
    > >>> + <MT2701_PIN_238_EXT_SDIO1__FUNC_EXT_SDIO1>,
    > >>> + <MT2701_PIN_237_EXT_SDIO2__FUNC_EXT_SDIO2>,
    > >>> + <MT2701_PIN_236_EXT_SDIO3__FUNC_EXT_SDIO3>;
    > >>> + drive-strength = <MTK_DRIVE_4mA>;
    > >>> + bias-pull-up;
    > >>> + };
    > >>> + };
    > >>> +};
    > >>> +
    > >>> &uart0 {
    > >>> status = "okay";
    > >>> };
    > >>> diff --git a/arch/arm/boot/dts/mt2701.dtsi
    > >>> b/arch/arm/boot/dts/mt2701.dtsi
    > >>> index bdf8954..1eefce4 100644
    > >>> --- a/arch/arm/boot/dts/mt2701.dtsi
    > >>> +++ b/arch/arm/boot/dts/mt2701.dtsi
    > >>> @@ -227,6 +227,18 @@
    > >>> status = "disabled";
    > >>> };
    > >>>
    > >>> + nor_flash: spi@11014000 {
    > >>> + compatible = "mediatek,mt2701-nor",
    > >>> + "mediatek,mt8173-nor";
    > >>
    > >> Why define both here? Is "mediatek,mt8173-nor" really providing a
    > >> subset of the features supported by "mediatek,mt2701-nor"?
    > >>
    > >
    > > I think even if the ip block is the same, we should provide both
    > > bindings, just in case in the future we find out that mt2701 has some
    > > hidden bug, feature or bug-feature. This way even if we update the
    > > driver, we stay compatible with older device tree blobs in the wild.
    > >
    > > We can drop the mt2701-nor in the bindings definition if you want.

    Oh, sorry, I misunderstood. What I meant is that if you want to
    list/support all possible compatibles, maybe you should just put one
    compatible in your DT and patch your driver (+ binding doc) to define
    all of them.

    >
    > This exactly. We should have a DT compat in the form:
    > compatible = "vendor,<soc>-block", "vendor,<oldest-compat-soc>-block";
    > Then if we find a problem in the future, we can match on the
    > "vendor,<soc>-block" and still support the old DTs.

    Not sure it's only in term of whose IP appeared first. My understanding
    is that it's a way to provide inheritance. For example:

    "<soc-vendor>,<ip-version>", "<ip-vendor>,<ip-version>";

    or

    "<soc-vendor>,<full-featured-ip-version>","<soc-vendor>,<basic-feature-ip-version>";

    BTW, which one is the oldest between mt8173 and mt2701? :-)

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