linux-kernel - Re: [PATCH 16/20] dt-bindings: memory: snps: Detach Zynq DDRC controller support

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Message-ID: <20220823114516.4mcufkbmzy5gjdcr@mobilestation>
Date:   Tue, 23 Aug 2022 14:45:16 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Rob Herring <robh@...nel.org>,
        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 16/20] dt-bindings: memory: snps: Detach Zynq DDRC
 controller support

On Tue, Aug 23, 2022 at 11:44:16AM +0300, Krzysztof Kozlowski wrote:
> On 23/08/2022 11:32, Serge Semin wrote:
> > On Tue, Aug 23, 2022 at 11:17:23AM +0300, Krzysztof Kozlowski wrote:
> >> On 22/08/2022 22:07, Serge Semin wrote:
> >>> The Zynq A05 DDRC controller has nothing in common with DW uMCTL2 DDRC:
> >>> the CSRs layout is absolutely different and it doesn't has IRQ unlike DW
> >>> uMCTL2 DDR controller of all versions (v1.x, v2.x and v3.x). Thus there is
> >>> no any reason to have these controllers described by the same bindings.
> >>> Thus let's split them up.
> >>>
> >>> While at it rename the original Synopsys uMCTL2 DT-schema file to a more
> >>> descriptive - snps,dw-umctl2-ddrc.yaml and add a more detailed title and
> >>> description of the device bindings.
> >>
> > 

> >> Filename should be based on compatible, so if renaming then
> >> snps,ddrc-3.80a.yaml or snps,ddrc.yaml... which leads to original
> >> filename anyway. Therefore nack for rename.

Original name was synopsys,ddrc-ecc.yaml which doesn't match any of
the compatible strings. 

> > 
> > New requirement? I've submitted not a single patch to the DT-bindings
> > sources and didn't get any comment from Rob about that. 
> 

> This is not a new requirement. It has been since some time and Rob gave
> such reviews.
> 
> https://lore.kernel.org/linux-devicetree/YlhkwvGdcf4ozTzG@robh.at.kernel.org/

April 2022. So it's new. It would be nice to have it defined somewhere
in docs (writing-bindings.rst?). So does the compatibles order (this
was surprising to me too).

> 
> For devices with multiple compatibles that's a bit tricky, but assuming
> the bindings describe both original design from Synopsys and it's
> implementations, then something closer to Synopsys makes sense.

The closest name would be snps,dw-umctl2-ddrc.yaml. snps,ddrc is too
generic especially for the IP-cores vendor. It doesn't have a
reference to the actual IP-core the device in subject is based on.

> 
> 
> > In addition
> > There are DT bindings with names different from what is defined in the
> > compatible name. Moreover there are tons of bindings with various
> > compatible names. What name to choose then? Finally the current name
> > is too generic to use for actual DW uMCTL2 DDRC controller.
> 

> There are thousands of bugs, inconsistencies, naming differences in
> kernel. I don't find these as arguments to repeat the practice...so the
> bindings file name should be based on the compatible.

Did I ask for an exception? I justified why the renaming was necessary. You
said it goes against the practice of having the DT-schema named as the
device compatible strings and just nacked. But above in this message you said

> "assuming the bindings describe both original design from Synopsys
> and it's implementations, then something closer to Synopsys makes sense"

What I suggest makes more sense than some abstract Synopsys DDRC,
which may refer to a Synopsys DDR controller other than the subject
one. So I see two solutions here:
1. Adding a new generic compatible string like "snps,dw-umctl2-ddrc"
and deprecate the "snps,ddrc-3.80a". It gets to be even more justified
seeing the Synopsys IP-core version has been exported in the device
CSRs since IP-core v3.20a. So having the version attached to the
compatible string was absolutely redundant.
2. Just deprecate the generic compatible string, the new compatible
devices will be supposed to use a vendor-specific compatible strings,
but still rename the DT-bindings file. This makes sense since the
current generic name isn't quiet well structured. It' prefix-part is
too generic and at the same time it refers to a device reversion for
no much reason.

What do you think?

* Note I've got it you'd prefer the renaming being performed in a
separate patch.

-Sergey

> 
> Best regards,
> Krzysztof