On Sun, 15 Jan 2017 01:23:48 +0100
Marek Vasut <marek.vasut@xxxxxxxxx> wrote:
> On 01/14/2017 09:29 AM, Boris Brezillon wrote:
> > On Fri, 13 Jan 2017 18:33:40 +0100
> > Marek Vasut <marek.vasut@xxxxxxxxx> wrote:
> >
> >> On 01/13/2017 05:56 PM, Boris Brezillon wrote:
> >>> 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 :-)
> >
> > 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 ?
The space you save by not growing the mtk_nor_of_ids table is lost in
your dtbs, so I'm not sure the size argument is relevant here. Also,
note that distros are shipping a lot of dtbs, and you're likely to have
several boards based on the mt2701 SoC, so, for this specific use case,
it's better to make the in-driver of-id table grow than specifying 2
compatibles in the DT. But as I said, I'm not sure we should rely on
this argument to decide which approach to choose (we're talking about a
few bytes 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
> >>
> >> 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 ...
>
Let's stop bikeshedding and wait for DT maintainers feedback
before taking a decision ;-).
Rob, Mark, any opinion?
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