On Sun, 15 Jan 2017 01:23:48 +0100
Marek Vasut [off-list ref] wrote:

On 01/14/2017 09:29 AM, Boris Brezillon wrote:

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On Fri, 13 Jan 2017 18:33:40 +0100
Marek Vasut [off-list ref] wrote:
  

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On 01/13/2017 05:56 PM, Boris Brezillon wrote:  

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On Fri, 13 Jan 2017 17:44:12 +0100
Marek Vasut [off-list ref] wrote:
    

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On 01/13/2017 05:28 PM, Boris Brezillon wrote:    

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On Fri, 13 Jan 2017 17:13:55 +0100
Marek Vasut [off-list ref] wrote:
      

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On 01/13/2017 04:12 PM, Matthias Brugger wrote:      

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On 13/01/17 15:17, Boris Brezillon wrote:        

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On Fri, 13 Jan 2017 15:13:29 +0800
Guochun Mao [off-list ref] wrote:
       

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Add Mediatek nor flash node.

Signed-off-by: Guochun Mao <redacted>
---
 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 at 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 at 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).

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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";
  

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	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?