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

[Marek Vasut <marek.vasut@gmail.com>]

On 01/14/2017 09:29 AM, Boris Brezillon wrote:
> On Fri, 13 Jan 2017 18:33:40 +0100
> Marek Vasut <marek.vasut@gmail.com> wrote:
> 
>> On 01/13/2017 05:56 PM, Boris Brezillon wrote:
>>> On Fri, 13 Jan 2017 17:44:12 +0100
>>> Marek Vasut <marek.vasut@gmail.com> wrote:
>>>   
>>>> On 01/13/2017 05:28 PM, Boris Brezillon wrote:  
>>>>> 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.    
>>>>
>>>> Uh, what ? I lost you here :-)
> 
> I mean adding a new entry in the mtk_nor_of_ids table (in
> mtk-quadspi.c) so that the mediatek,mt2701-nor compatible string can be
> matched directly, and you won't need to define 2 compatible strings in
> your device tree.

But then you grow the table in the driver, is that what we want if we
can avoid that ?

>>>>  
>>>>>> 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";  
>>>
>>> I'd say
>>>
>>> 	compatible = "mediatek,mt8173-nor";
>>>
>>> because both compatible are referring to very specific IP version. It's
>>> not the same as  
>>
>> But then you don't have the ability to handle a block in this particular
>> SoC in case there's a bug found in it in the future,
>> so IMO it should be:
>>
>> compatible = "mediatek,mt2701-nor", "mediatek,mt8173-nor";
> 
> Sorry again, I meant
> 
> 	compatible = "mediatek,mt2701-nor";
> 
>>
>>> 	compatible = "mediatek,mt8173-nor", "mediatek,mt81xx-nor";  
>>
>> This doesn't look right, since here we add two new compatibles ...
> 
> That was just an example to describe how compatible inheritance works
> (at least that's my understanding of it), it does not apply to this
> particular use case.

Well this is OK I guess, but then you can also use "mediatek,mt8173-nor"
as the oldest supported compatible and be done with it, no ? It looks a
bit crappy though, I admit that ...

-- 
Best regards,
Marek Vasut