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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>,
	Odelu Kukatla <okukatla@codeaurora.org>
Subject: Re: [PATCH V2] arm64: dts: qcom: sc7280: Add nodes for eMMC and SD card
Date: Tue, 20 Apr 2021 13:14:18 -0700	[thread overview]
Message-ID: <CAD=FV=U0zEDi1Xn3OmVFA3h3maVWS_o2FXOW9qDEzTf1Moja=A@mail.gmail.com> (raw)
In-Reply-To: <32096a375966e1fcc149016df012c445@codeaurora.org>

Hi,

On Tue, Apr 20, 2021 at 10:21 AM <sbhanu@codeaurora.org> wrote:
>
> On 2021-04-15 01:55, Doug Anderson wrote:
> > 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.
> >
>
> ICB team has re-checked the Rennell ICB tool and they confirmed that
> some configs were wrong in Rennell ICB tool and they corrected it.With
> the new updated Rennell ICB tool below are the values :
>
>
> Rennell LC:(Sc7180)
>
> opp-384000000 {
>               opp-hz = /bits/ 64 <384000000>;
>               required-opps = <&rpmhpd_opp_nom>;
>               opp-peak-kBps = <5400000 490000>;
>               opp-avg-kBps = <6600000 300000>;
> };
>
>
> And now, these values are near to Kodaik LC values:
>
> Kodaik LC:(SC7280)
>
> opp-384000000 {
>             opp-hz = /bits/ 64 <384000000>;
>             required-opps = <&rpmhpd_opp_nom>;
>             opp-peak-kBps = <5400000 399000>;
>             opp-avg-kBps = <6000000 300000>;
> };

This still isn't making sense to me.

* sc7180 and sc7280 are running at the same speed. I'm glad the
numbers are closer now, but I would have thought they'd be exactly the
same.

* Aren't these supposed to be sensible? This is eMMC that does max
transfer rates of 400 megabytes / second to the external device. You
have bandwidths listed here of 5,400,000 kBps = 5,400,000 kilobytes /
second = 5400 megabytes / second. I can imagine there being some
overhead where an internal bus might need to be faster but that seems
excessive. This is 13.5x!

* I can't see how it can make sense that "average" values are higher
than "peak" values.

It still feels like there's a misconfiguration somewhere.

-Doug

  reply	other threads:[~2021-04-20 20:14 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-20 18:17 [PATCH V2] arm64: dts: qcom: sc7280: Add nodes for eMMC and SD card Shaik Sajida Bhanu
2021-03-23  7:01 ` Stephen Boyd
2021-03-24 15:23   ` sbhanu
2021-03-24 15:57     ` Stephen Boyd
2021-03-24 16:28       ` Stephen Boyd
2021-03-25  3:36         ` Veerabhadrarao Badiganti
2021-03-25 16:20           ` Doug Anderson
2021-03-23 16:11 ` Doug Anderson
2021-03-25  3:58   ` Veerabhadrarao Badiganti
2021-03-25 16:17     ` Doug Anderson
2021-04-01  9:58       ` sbhanu
2021-03-26  6:56     ` sbhanu
2021-03-29 14:56       ` Doug Anderson
2021-04-13 10:59         ` sbhanu
2021-04-14 20:25           ` Doug Anderson
2021-04-16  9:52             ` Georgi Djakov
2021-04-20 17:20             ` sbhanu
2021-04-20 20:14               ` Doug Anderson [this message]
2021-04-28 10:47                 ` sbhanu
2021-04-28 15:13                   ` Doug Anderson
2021-04-29 20:44                     ` Georgi Djakov
2021-06-01  9:58                       ` sbhanu

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