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

From: Doug Anderson <dianders@google.com>
To: Shaik Sajida Bhanu <sbhanu@codeaurora.org>
Cc: Veerabhadrarao Badiganti <vbadigan@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>,
	Evan Green <evgreen@chromium.org>,
	Georgi Djakov <georgi.djakov@linaro.org>
Subject: Re: [PATCH V2] arm64: dts: qcom: sc7280: Add nodes for eMMC and SD card
Date: Wed, 14 Apr 2021 13:25:58 -0700	[thread overview]
Message-ID: <CAD=FV=XavWbf_b7-=JT6V5_RNA8CjdK4oRu7H719AaPDJ5tsqQ@mail.gmail.com> (raw)
In-Reply-To: <8126e130e5c0ea1e7ea867414f0510c0@codeaurora.org>

Hi,

On Tue, Apr 13, 2021 at 3:59 AM <sbhanu@codeaurora.org> wrote:
>
> >> >>> +                                       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.
> >
> we checked with ICB tool team on this they conformed as Rennell & Kodiak
> are different chipsets,
> we might see delta in ib/ab values due to delta in scaling factors.

...but these numbers are in kbps, aren't they? As I understand it
these aren't supposed to be random numbers spit out by a tool but are
supposed to be understandable by how much bandwidth an IP block (like
MMC) needs from the busses it's connected to. Since the MMC IP block
on sc7180 and sc7280 is roughly the same there shouldn't be a big
difference in numbers.

Something smells wrong.

Adding a few people who understand interconnects better than I do, though.

-Doug