linux-kernel - Re: [PATCH] interconnect: qcom: use icc_sync

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Date:   Thu, 28 Apr 2022 12:23:09 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Georgi Djakov <djakov@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] interconnect: qcom: use icc_sync_state

On 27/04/2022 17:34, Georgi Djakov wrote:
> On 27.04.22 17:56, Krzysztof Kozlowski wrote:
>> Use icc_sync_state for interconnect providers, so that the bandwidth
>> request doesn't need to stay on maximum value.
> 
> Did you test this? In general, we should not enable this on boards that
> do not have full interconnect scaling support in consumer drivers yet.
> Some of the interconnects could be enabled by default by the bootloader
> and usually later during boot the consumer drivers request the bandwidth
> that they need. But if the requests are missing, the interconnects
> without bandwidth users will be disabled when we reach sync state. So
> this may (or not) cause issues...

I understand, thanks for bringing this up. It does not look like an
issue of interconnect provider but instead consumers and DTS. It's not
the job of provider driver to know all possible uses and DTS files. The
driver should expose itself and if platform is not ready, should not use
it by not enabling the interconnect. It's a job for DTS, not for the
interconnect provider.

Imagine some out of tree DTS which cannot use interconnects because we
assume that all users of that provider are missing bandwidth requests.
No, instead provider should allow anyone to use it.

I understand my change might cause unexpected issues, but it is still
technically correct, just maybe should be followed with disabling in DTS
the providers without proper consumers?

Best regards,
Krzysztof