linux-kernel - Re: [PATCH 02/13] dt-bindings: memory: snps: Add Baikal-T1 DDRC support

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Message-ID: <20220826095447.qxfvty6xq4tufe75@mobilestation>
Date:   Fri, 26 Aug 2022 12:54:47 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Michal Simek <michal.simek@...inx.com>,
        Borislav Petkov <bp@...en8.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Manish Narani <manish.narani@...inx.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Michail Ivanov <Michail.Ivanov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Punnaiah Choudary Kalluri 
        <punnaiah.choudary.kalluri@...inx.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] dt-bindings: memory: snps: Add Baikal-T1 DDRC
 support

On Tue, Aug 23, 2022 at 11:12:28AM +0300, Krzysztof Kozlowski wrote:
> On 22/08/2022 22:19, Serge Semin wrote:
> > Baikal-T1 DDR controller is based on the DW uMCTL2 DDRC IP-core v2.51a
> > with up to DDR3 protocol capability and 32-bit data bus + 8-bit ECC. There
> > are individual IRQs for each ECC and DFI events.The dedicated scrubber
> 

> Missing space before "The".

Ok. Thanks.

> 
> > clock source is absent since it's fully synchronous to the core clock.
> 

> You need allOf:if-then restricting this per variant.

I really don't like the allOf-if-if-etc pattern because it gets to be
very bulky if all the vendor-specific and generic platform
peculiarities are placed in there. I am more keen of having a
generic DT-schema which would be then allOf-ed by the vendor-specific
device bindings. What do you think I'd provide such design in this
case too?

But I'll need to move the compatible property definition to the
"select" property. Like this:

Documentation/devicetree/bindings/memory-controllers/snps,dw-umctl2-ddrc.yaml:
+[...]
+# Please create a separate DT-schema for your DW uMCTL2 DDR controller
+# and make sure it's assigned with the vendor-specific compatible string.
+select:
+  properties:
+    compatible:
+      oneOf:
+        - deprecated: true
+          description: Synopsys DW uMCTL2 DDR controller v3.80a
+          const: snps,ddrc-3.80a
+        - description: Synopsys DW uMCTL2 DDR controller
+          const: snps,dw-umctl2-ddrc
+        - description: Xilinx ZynqMP DDR controller v2.40a
+          const: xlnx,zynqmp-ddrc-2.40a
+  required:
+    - compatible
+
+properties:
+  compatible: true
+[...]
+required:
+  - compatible
+  - reg
+  - interrupts
+
+additionalProperties: true

After that the "snps,dw-umctl2-ddrc.yaml" schema can be referenced in the
allOf composition. Like this:

Documentation/devicetree/bindings/memory-controllers/baikal,bt1-ddrc.yaml:
+[...]
+allOf:
+  - $ref: /schemas/memory-controllers/snps,dw-umctl2-ddrc.yaml#
+[...]

At the same time the generic DT-schema will be used to evaluate the
"snps,ddrc-3.80a", "snps,dw-umctl2-ddrc" and "xlnx,zynqmp-ddrc-2.40a"
device nodes as before. What do you think about that?

One big positive side of this that even though the generic schema
can't define the IRQ/resets/clocks phandlers order because various
platforms may have different external signals setup, the
vendor-specific schema can and should. So I'll be able to describe the
Baikal-T1 DDRC specific properties (clocks, clock-names, interrupts,
interrupt-names, etc) in much more details including the reference
signals order what you asked in the previous patch review.

-Sergey

> 
> > In addition to that the DFI-DDR PHY CSRs can be accessed via a separate
> > registers space.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > ---
> >  .../memory-controllers/snps,dw-umctl2-ddrc.yaml        | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/memory-controllers/snps,dw-umctl2-ddrc.yaml b/Documentation/devicetree/bindings/memory-controllers/snps,dw-umctl2-ddrc.yaml
> > index 8db92210cfe1..899a6c5f9806 100644
> > --- a/Documentation/devicetree/bindings/memory-controllers/snps,dw-umctl2-ddrc.yaml
> > +++ b/Documentation/devicetree/bindings/memory-controllers/snps,dw-umctl2-ddrc.yaml
> > @@ -26,6 +26,7 @@ properties:
> >      enum:
> >        - snps,ddrc-3.80a
> >        - xlnx,zynqmp-ddrc-2.40a
> > +      - baikal,bt1-ddrc
>
 
> Messed order. Don't add stuff at the end, but in alphabetical order.

Ok. But could you please give me a reference with this requirement
documented? I've submitted many DT-bindings patches with the
compatible property updates and none of them received such comment
from Rob.

> 
> >  
> >    interrupts:
> >      description:
> > @@ -49,7 +50,14 @@ properties:
> >            enum: [ ecc_ce, ecc_ue, ecc_ap, ecc_sbr, dfi_e ]
> >  
> >    reg:
> > -    maxItems: 1
> > +    minItems: 1
> > +    maxItems: 2
> > +
> > +  reg-names:
> > +    minItems: 1
> > +    items:
> > +      - const: umctl2
> > +      - const: phy
> 

> You need allOf:if-then restricting this per variant.

Please see my comment above regarding possible solution of this.

-Sergey

> 
> Best regards,
> Krzysztof