linux-kernel - Re: [PATCH V5 2/4] dt-bindings: mmc: controller: Add max-sd-hs-frequency property

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Message-ID: <20250903203928.GA2663015-robh@kernel.org>
Date: Wed, 3 Sep 2025 15:39:28 -0500
From: Rob Herring <robh@...nel.org>
To: Sarthak Garg <quic_sartgarg@...cinc.com>
Cc: Ulf Hansson <ulf.hansson@...aro.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>, linux-mmc@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, quic_nguyenb@...cinc.com,
	quic_rampraka@...cinc.com, quic_pragalla@...cinc.com,
	quic_sayalil@...cinc.com, quic_nitirawa@...cinc.com,
	quic_bhaskarv@...cinc.com, kernel@....qualcomm.com
Subject: Re: [PATCH V5 2/4] dt-bindings: mmc: controller: Add
 max-sd-hs-frequency property

On Wed, Sep 03, 2025 at 01:34:02PM +0530, Sarthak Garg wrote:
> Some platforms may require limiting the maximum frequency used in SD
> High-Speed (HS) mode due to board-level hardware constraints. For
> example, certain boards may include level shifters or other components
> that cannot reliably operate at the default 50 MHz HS frequency.
> 
> Introduce a new optional device tree property max-sd-hs-frequency to
> limit the maximum frequency (in Hz) used for SD cards operating in
> High-Speed (HS) mode.
> 
> Signed-off-by: Sarthak Garg <quic_sartgarg@...cinc.com>
> ---
>  .../devicetree/bindings/mmc/mmc-controller-common.yaml    | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
> index 9a7235439759..d6b785cb2bd9 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
> +++ b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
> @@ -93,6 +93,14 @@ properties:
>      minimum: 400000
>      maximum: 384000000
>  
> +  max-sd-hs-hz:
> +    description: |
> +      Maximum frequency (in Hz) to be used for SD cards operating in
> +      High-Speed (HS) mode. This is useful for board-specific limitations,
> +      such as level shifters or others where the card cannot reliably
> +      operate at the default 50 MHz HS frequency.
> +    default: 50000000

Why doesn't max-frequency work for you? I would think frequency limits 
wouldn't really depend on the mode.

> +
>    disable-wp:
>      $ref: /schemas/types.yaml#/definitions/flag
>      description:
> -- 
> 2.34.1
>