Re: [PATCH v4 1/3] arm64: dts: qcom: sc7280: Add proxy interconnect requirements for modem

[Sibi Sankar <quic_sibis@quicinc.com>]

On 5/21/22 12:37 AM, Stephen Boyd wrote:
> Quoting Sibi Sankar (2022-05-20 11:08:52)
>> Hey Bjorn,
>> Thanks for taking time to review the series.
>>
>> On 5/20/22 2:05 AM, Bjorn Andersson wrote:
>>> On Thu 19 May 09:47 PDT 2022, Sibi Sankar wrote:
>>>
>>>> Add interconnects that are required to be proxy voted upon during modem
>>>> bootup on SC7280 SoCs.
>>>
>>> This looks reasonable, but how come the vote is only for DDR frequency?
>>> What about the buses between modem and ddr?
>>
>> The proxy votes that are put in aren't for perf related reasons, the
>> modem was getting llcc timeouts while trying to read contents from
>> memory. The hw team recommended the proxy votes as the fix.
> 
> Presumably the bootloader sets up some initial modem and ddr bus
> bandwidth requests? Or the modem bootloader stage (MSA?) handles that
> part?

Stephen/Bjorn,
Sorry for the delay, took a while to dig this up. The modem interconnect
is connected directly to gemnoc ddr. The path info from modem --> ddr is
split up into modem --> llcc and llcc --> ddr (Similar to CPUs) i.e. in
the end scaling of the path involves scaling of the two clocks, gemnoc
and ddr. There isn't any default vote for modem --> llcc as such but it
gets implicitly scaled when we vote max for llcc --> ddr path due to
dependency maintained between the two clocks by rpmh.

-Sibi

>