linux-kernel - Re: [PATCH RFC v2 1/4] dt-bindings: mmc: sdhci-of-dwcmhsc: Add T-Head TH1520 support

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Message-ID: <2de9f105-c785-4933-4a0f-c8bc73c63b87@linaro.org>
Date:   Sat, 19 Aug 2023 15:06:37 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Drew Fustini <dfustini@...libre.com>
Cc:     Jisheng Zhang <jszhang@...nel.org>, Guo Ren <guoren@...nel.org>,
        Fu Wei <wefu@...hat.com>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Conor Dooley <conor@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
        Robert Nelson <robertcnelson@...gleboard.org>,
        Jason Kridner <jkridner@...gleboard.org>
Subject: Re: [PATCH RFC v2 1/4] dt-bindings: mmc: sdhci-of-dwcmhsc: Add T-Head
 TH1520 support

On 17/08/2023 00:26, Drew Fustini wrote:
> On Mon, Aug 07, 2023 at 08:29:21AM +0200, Krzysztof Kozlowski wrote:
>> On 05/08/2023 05:14, Drew Fustini wrote:
>>> Add compatible value for the T-Head TH1520 dwcmshc controller and
>>> thead,io-fixed-1v8 and thead,pull-up properties.
>>>
>>> Signed-off-by: Drew Fustini <dfustini@...libre.com>
>>> ---
>>>  Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml | 9 +++++++++
>>>  1 file changed, 9 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml b/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml
>>> index a43eb837f8da..57602c345cab 100644
>>> --- a/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml
>>> +++ b/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml
>>> @@ -19,6 +19,7 @@ properties:
>>>        - rockchip,rk3568-dwcmshc
>>>        - rockchip,rk3588-dwcmshc
>>>        - snps,dwcmshc-sdhci
>>> +      - thead,th1520-dwcmshc
>>>  
>>>    reg:
>>>      maxItems: 1
>>> @@ -60,6 +61,14 @@ properties:
>>>      description: Specify the number of delay for tx sampling.
>>>      $ref: /schemas/types.yaml#/definitions/uint8
>>>  
>>> +  thead,io-fixed-1v8:
>>> +    description: SoC PHY pad is fixed 1.8V
>>> +    type: boolean
>>
>> Isn't this duplicating existing properties for MMC modes with 1.8 V?
> 
> Thank you for reviewing. Yes, now that you mention it, I do see those
> properties now in mmc-controller.yaml. It seems like the existing
> mmc-ddr-1_8v property would be appropriate.
> 
>>
>>> +
>>> +  thead,pull-up:
>>> +    description: True if pull-up, false if pull-down
>>
>> This explains me nothing. No clue what you are pulling and why do you
>> need it. Pin pulls should be done via pin controller, not MMC.
> 
> Good point that my description is not helpful. The pull-up property
> determines whether certain phy registers are written to. I need to try
> to can get documentation on the phy so that I can better understand the
> details of the pull-up configuration in the phy registers.
> 
>>
>> Anyway you should have here allOf:if:then (move the allOf: from top to
>> behind "required:") which will disallow these properties for other variants.
> 
> I noticed that nvidia,tegra20-sdhci.yaml has several lines related to
> pull-up/down configuration:
> 
> 218   - if:
> 219       properties:
> 220         compatible:
> 221           contains:
> 222             const: nvidia,tegra210-sdhci
> 223     then:
> 224       properties:
> 225         pinctrl-names:
> 226           oneOf:
> 227             - items:
> 228                 - const: sdmmc-3v3
> 229                   description: pad configuration for 3.3 V
> 230                 - const: sdmmc-1v8
> 231                   description: pad configuration for 1.8 V
> 232                 - const: sdmmc-3v3-drv
> 233                   description: pull-up/down configuration for 3.3 V
> 234                 - const: sdmmc-1v8-drv
> 235                   description: pull-up/down configuration for 1.8 V
> 236             - items:
> 237                 - const: sdmmc-3v3-drv
> 238                   description: pull-up/down configuration for 3.3 V
> 239                 - const: sdmmc-1v8-drv
> 240                   description: pull-up/down configuration for 1.8 V
> 241             - items:
> 242                 - const: sdmmc-1v8-drv
> 243                   description: pull-up/down configuration for 1.8 V
> 
> Do you think creating something like that would be a good approach?

This depends. Does your driver implementation will make use of it? If
yes, then it makes sense.

Best regards,
Krzysztof