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

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Date:   Thu, 01 Apr 2021 15:28:34 +0530
From:   sbhanu@...eaurora.org
To:     Doug Anderson <dianders@...gle.com>
Cc:     Veerabhadrarao Badiganti <vbadigan@...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

On 2021-03-25 21:47, Doug Anderson wrote:
> 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?
sure will 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.
> 
sure will remove these for SD card and will move eMMC flags(no-sd and 
no-sdio) to board dts file.
> 
> -Doug