linux-kernel - Re: [PATCH] dt-bindings: mmc: Add cap-aggressive-pm property

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Date:   Thu, 2 Feb 2023 15:59:25 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Hermes Zhang <chenhuiz@...s.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        kernel@...s.com, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: mmc: Add cap-aggressive-pm property

On Tue, 31 Jan 2023 at 17:57, Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 30/01/2023 07:54, Hermes Zhang wrote:
> > On 2023/1/29 18:58, Krzysztof Kozlowski wrote:
> >> On 29/01/2023 03:36, Hermes Zhang wrote:
> >>> This commit add a new property: cap-aggressive-pm to enable the
> >> Do not use "This commit/patch".
> >> https://elixir.bootlin.com/linux/v5.17.1/source/Documentation/process/submitting-patches.rst#L95
> >
> > Done
> >
> >>> MMC_CAP_AGGRESSIVE_PM feature for (e)MMC/SD power saving.
> >> Why this is a property suitable for DT? IOW, why this isn't enabled always?
> >
> > This property will benfit for the power consumption, but it also may
> > degradation in performance as it will prevent the
> >
> > the card from executing internal house-keeping operations in idle mode.
> > So it's better to config it from DT.
>
> Why? DT is not for policy. How you described it, this is policy or
> system tuning choice thus the job for Linux (OS), not for DT. So I will
> repeat - why this property fits the purpose of DT (describe the hardware).
>

I guess the HW perspective here, is that it might not fit all
platforms nor the actual eMMC/SD card to support this feature.
However, it still seems like a policy rather than a strict HW
constraint.

Perhaps there is a way to figure out in the host driver, to
conditionally set the MMC_CAP_AGGRESSIVE_PM for the host, when needed
instead?

Kind regards
Uffe