linux-kernel - Re: [PATCH v1 2/2] arm: dts: mt2701: add nor flash node

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Message-ID: <86c997be-f500-eaa1-3ba5-d21cff6223b7@gmail.com>
Date:   Fri, 13 Jan 2017 17:44:12 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Guochun Mao <guochun.mao@...iatek.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] arm: dts: mt2701: add nor flash node

On 01/13/2017 05:28 PM, Boris Brezillon wrote:
> On Fri, 13 Jan 2017 17:13:55 +0100
> Marek Vasut <marek.vasut@...il.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@...iatek.com> wrote:
>>>>  
>>>>> Add Mediatek nor flash node.
>>>>>
>>>>> Signed-off-by: Guochun Mao <guochun.mao@...iatek.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@...14000 {
>>>>> +        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.

Uh, what ? I lost you here :-)

>> 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? :-)

And that's another thing and I agree with you, but I don't think that's
what we're discussing in this thread. But (!), OT, I think we should
codify the rules in Documentation/ . This discussion came up multiple
times recently.

And my question still stands, what do we put into the DT here, IMO
compatible = "mediatek,mt2701-nor", "mediatek,mt8173-nor";
and what goes into the binding document ? I guess both too ?
-- 
Best regards,
Marek Vasut