linux-kernel - Re: [PATCH v2 2/3] dt-bindings: mmc: Add a new property disable-cqe-dcmd.

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Message-ID: <4793843.T1TZ7EF8k3@phil>
Date:   Tue, 12 Mar 2019 14:17:55 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Christoph Müllner 
        <christoph.muellner@...obroma-systems.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>, robh+dt@...nel.org,
        mark.rutland@....com, shawn.lin@...k-chips.com,
        ulf.hansson@...aro.org,
        Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
        Michal Simek <michal.simek@...inx.com>,
        Douglas Anderson <dianders@...omium.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Vicente Bergas <vicencb@...il.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Randy Li <ayaka@...lik.info>,
        Tony Xie <tony.xie@...k-chips.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Klaus Goger <klaus.goger@...obroma-systems.com>,
        Lin Huang <hl@...k-chips.com>, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v2 2/3] dt-bindings: mmc: Add a new property disable-cqe-dcmd.

Am Freitag, 8. März 2019, 14:10:45 CET schrieb Christoph Müllner:
> 
> > On 08.03.2019, at 13:46, Adrian Hunter <adrian.hunter@...el.com> wrote:
> > 
> > On 7/03/19 10:43 AM, Christoph Muellner wrote:
> >> This patch documents the new property disable-cqe-dcmd
> >> for the Arasan eMMC 5.1 driver.
> >> 
> >> Signed-off-by: Christoph Muellner <christoph.muellner@...obroma-systems.com>
> >> Signed-off-by: Philipp Tomsich <philipp.tomsich@...obroma-systems.com>
> >> ---
> >> Documentation/devicetree/bindings/mmc/arasan,sdhci.txt | 4 ++++
> >> 1 file changed, 4 insertions(+)
> >> 
> >> diff --git a/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt b/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
> >> index 1edbb049cccb..ec699bf98b7c 100644
> >> --- a/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
> >> +++ b/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
> >> @@ -44,6 +44,10 @@ Optional Properties:
> >>     properly. Test mode can be used to force the controller to function.
> >>   - xlnx,int-clock-stable-broken: when present, the controller always reports
> >>     that the internal clock is stable even when it is not.
> >> +  - disable-cqe-dcmd: The eMMC 5.1 standard specifies direct commands (DCMDs)
> >> +    as part of the command queue engine (CQE). On controllers with a CQHCI,
> >> +    such as the Arasan eMMC 5.1 host controller, the driver has to enable DCMDs.
> >> +    This is done unless disable-cqe-dcmd is specified.

This needs a rewording please. See below for hw-description vs. driver, so
the description should be centered around why this is a property of the hw
[like faulty controller implementation or whatever]


> > If "supports-cqe" is in mmc.txt, should "disable-cqe-dcmd" be there also?
> 
> The file mmc.txt says on top:
> "These properties are common to multiple MMC host controllers".
> As my patchset introduces "disable-cqe-dcmd" just for sdhci-of-arasan,
> I would say it should not go into that file.
> 
> Also I wonder why "supports-cqe" is in mmc.txt, because
> only sdhci-tegra.c is evaluating that property.
> So I would expect it to be documented in
> Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt
> 
> However, I see that "disable-cqe-dcmd" could go into other drivers as well.
> But is this enough to document it in mmc.txt?

Devicetree is always about describing the hardware capabilites and never
about the actual nitty-gritty of driver implementation, aka it is not meant
as a space for hardware-independent config-settings or such.

As for only tegra evaluating this, is probably because it is still so new, like
january 2019 and Rob explicitly suggested it becoming common [0], which
suggests that the disable-cqe-dcmds should probably also be common.

Heiko

[0] https://lore.kernel.org/patchwork/patch/1031163/