linux-kernel - Re: [PATCH v2 4/4] arm64: dts: qcom: sc7280: Add cpu and llcc BWMON (=> interconnect issue)

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Message-ID: <dc5487d8-d31e-28c6-07e8-8d1ff54a4ba4@linaro.org>
Date:   Sun, 15 Jan 2023 16:13:40 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Rajendra Nayak <quic_rjendra@...cinc.com>,
        Georgi Djakov <djakov@...nel.org>
Cc:     agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...ainline.org, robh+dt@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v2 4/4] arm64: dts: qcom: sc7280: Add cpu and llcc BWMON
 (=> interconnect issue)

On 13/01/2023 19:18, Matthias Kaehlcke wrote:
> Hi,
> 
> On Fri, Sep 02, 2022 at 10:05:11AM +0530, Rajendra Nayak wrote:
>> Add cpu and llcc BWMON nodes and their corresponding
>> OPP tables for sc7280 SoC.
>>
>> Signed-off-by: Rajendra Nayak <quic_rjendra@...cinc.com>
>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> 
> I found that with a v6.1 kernel AOSS on sc7280 doesn't reach it's low
> power state during system. This can be observed on herobrine based
> boards on which the AP_SUSPEND signal should transition to 1 during
> system suspend. If it doesn't the Embedded Controller (EC) notices
> it and wakes the system up again.
> 
> Bisection points to this patch, the issue only occurs when
> CONFIG_QCOM_ICC_BWMON is *not* set. One might think the patch shouldn't
> have any impact at all when the driver is not enabled, but it does.
> 
> Debugging shows that the issue is interconnect related. A bare platform
> device is created for each bwmon devices, which results in the average
> and peak bandwidth of the interconnect link to be set 'initially' to
> INT_MAX. The driver is supposed to call icc_sync_state() during probe,

This is for interconnect providers, not consumers.

> which would set the initially bandwidths to 0 and determine the actually
> needed bandwidth. But since the driver isn't probed the initial
> bandwidths stay at INT_MAX.
> 
> This isn't actually an issue with this patch, but how the interconnect
> framework deals with devices that are registered on the bus, but aren't
> probed (yet). Not sure how this would be best fixed. Georgi, do you have
> any ideas?

Why the device is not probed (yet)? If it is registered, it will come
soon during boot up.

Best regards,
Krzysztof