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

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Date:   Mon, 29 Mar 2021 07:56:52 -0700
From:   Doug Anderson <dianders@...gle.com>
To:     Shaik Sajida Bhanu <sbhanu@...eaurora.org>
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

Hi,

On Thu, Mar 25, 2021 at 11:57 PM <sbhanu@...eaurora.org> wrote:
>
> >>> +                       max-frequency = <192000000>;
> >> Why do you need to specify this?
> This helps to avoid lower speed modes running in high clock rate,
> and As Veerabhadrarao Badiganti mentioned

Just to be clear, both Stephen and I agree that you should remove
"max-frequency" here (see previous discussion). Bjorn is, of course,
the file decision maker. However, unless he says "yeah, totally keep
it in" I'd suggest dropping it from the next version.


> >>> +                                       required-opps =
> >>> <&rpmhpd_opp_low_svs>;
> >>> +                                       opp-peak-kBps = <1200000
> >>> 76000>;
> >>> +                                       opp-avg-kBps = <1200000
> >>> 50000>;
> >> Why are the kBps numbers so vastly different than the ones on sc7180
> >> for the same OPP point. That implies:
> >>
> >> a) sc7180 is wrong.
> >>
> >> b) This patch is wrong.
> >>
> >> c) The numbers are essentially random and don't really matter.
> >>
> >> Can you identify which of a), b), or c) is correct, or propose an
> >> alternate explanation of the difference?
> >>
>
> We calculated bus votes values for both sc7180 and sc7280 with ICB tool,
> above mentioned values we got for sc7280.

I don't know what an ICB tool is. Please clarify.

Also: just because a tool spits out numbers that doesn't mean it's
correct. Presumably the tool could be wrong or incorrectly configured.
We need to understand why these numbers are different.

-Doug