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

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Hi,

On 14.04.21 23:25, Doug Anderson wrote:
Hi,

On Tue, Apr 13, 2021 at 3:59 AM <sbhanu@xxxxxxxxxxxxxx> 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.

If the scaling factor is different, maybe this should be reflected
in the BCM data, where we have the following:
    @vote_scale: scaling factor for vote_x and vote_y

This is 1000 by default, but maybe we should set it to some
different value for some of the BCMs?

I'm adding Odelu, who is more familiar with this platform.


...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.


Thanks!
Georgi



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