linux-kernel - Re: [PATCH V2] arm64: dts: qcom: sc7280: Add nodes for eMMC and SD card

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Date:   Thu, 25 Mar 2021 09:17:57 -0700
From:   Doug Anderson <dianders@...gle.com>
To:     Veerabhadrarao Badiganti <vbadigan@...eaurora.org>
Cc:     Shaik Sajida Bhanu <sbhanu@...eaurora.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Ram Prakash Gupta <rampraka@...eaurora.org>,
        Sayali Lokhande <sayalil@...eaurora.org>,
        sartgarg@...eaurora.org, Rajendra Nayak <rnayak@...eaurora.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>, cang@...eaurora.org,
        pragalla@...eaurora.org, nitirawa@...eaurora.org,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH V2] arm64: dts: qcom: sc7280: Add nodes for eMMC and SD card

Hi,

On Wed, Mar 24, 2021 at 8:59 PM Veerabhadrarao Badiganti
<vbadigan@...eaurora.org> wrote:
>
> >> +                       clocks = <&gcc GCC_SDCC1_APPS_CLK>,
> >> +                                       <&gcc GCC_SDCC1_AHB_CLK>,
> >> +                                       <&rpmhcc RPMH_CXO_CLK>;
> >> +                       clock-names = "core", "iface", "xo";
> > I'm curious: why is the "xo" clock needed here but not for sc7180?
> Actually its needed even for sc7180. We are making use of this clock in
> msm_init_cm_dll()
> The default PoR value is also same as calculated value for
> HS200/HS400/SDR104 modes.
> But just not to rely on default register values we need this entry.

Can you post a patch for sc7180?


> >> +                       bus-width = <4>;
> >> +
> >> +                       no-mmc;
> >> +                       no-sdio;
> > Similar question to above: why exactly would mmc not work? Are you
> > saying that if someone hooked this up to a full sized SD card slot and
> > placed an MMC card into the slot that it wouldn't work? Similar
> > question about SDIO. If someone placed an external SDIO card into your
> > slot, would it not work?
> >
> As mentioned above, its just to optimize SDcard scan time a little.

OK. ...but while the eMMC one can make sense since the eMMC is
soldered down (but in the board dts file, not in the SoC dtsi file) I
think you should just remove these for SD card because:

1. Even if only a uSD slot is exposed it's still _possible_ for
someone to insert a card that uses MMC or SDIO signaling. If nothing
else I have a (probably non-compliant) adapter that plugs into a uSD
slot and provides a full sided SD slot. I could plug an MMC card or
SDIO card in.

2. Presumably the SD card scan time optimization is tiny.


-Doug