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

[Boris Brezillon]

On Fri, 13 Jan 2017 17:44:12 +0100
Marek Vasut <marek.vasut@xxxxxxxxx> wrote:

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

	compatible = "mediatek,mt8173-nor", "mediatek,mt81xx-nor";

where you clearly have a generic compatible which is overloaded by a
specific one.

But anyway, I'm not the one taking the decision here, let's wait for DT
maintainers reviews.

> and what goes into the binding document ? I guess both too ?

If both exist, they should be both documented.