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

From: Doug Anderson <dianders@google.com>
To: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>
Cc: Shaik Sajida Bhanu <sbhanu@codeaurora.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Asutosh Das <asutoshd@codeaurora.org>,
	Sahitya Tummala <stummala@codeaurora.org>,
	Ram Prakash Gupta <rampraka@codeaurora.org>,
	Sayali Lokhande <sayalil@codeaurora.org>,
	sartgarg@codeaurora.org, Rajendra Nayak <rnayak@codeaurora.org>,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	Sibi Sankar <sibis@codeaurora.org>,
	cang@codeaurora.org, pragalla@codeaurora.org,
	nitirawa@codeaurora.org,
	Linux MMC List <linux-mmc@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>, Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>
Subject: Re: [PATCH V2] arm64: dts: qcom: sc7280: Add nodes for eMMC and SD card
Date: Thu, 25 Mar 2021 09:17:57 -0700	[thread overview]
Message-ID: <CAD=FV=ULXU46C4jbx4nJEOuK4+wZmknoD=mZ_3=c0drfa32N=w@mail.gmail.com> (raw)
In-Reply-To: <b77f207b-2d90-3c8b-857f-625bd3867ed1@codeaurora.org>

Hi,

On Wed, Mar 24, 2021 at 8:59 PM Veerabhadrarao Badiganti
<vbadigan@codeaurora.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