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Date: Fri, 13 Jan 2017 17:56:28 +0100
From: Boris Brezillon <boris.brezillon@...e-electrons.com>
To: Marek Vasut <marek.vasut@...il.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 Fri, 13 Jan 2017 17:44:12 +0100
Marek Vasut <marek.vasut@...il.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@...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";
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.
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