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

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Message-ID: <Y8baZWlKB9vNGYJw@google.com>
Date:   Tue, 17 Jan 2023 17:27:01 +0000
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Rajendra Nayak <quic_rjendra@...cinc.com>,
        Georgi Djakov <djakov@...nel.org>, 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 Sun, Jan 15, 2023 at 04:13:40PM +0100, Krzysztof Kozlowski wrote:
> 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.

Ah, thanks for the clarification.

Still, for the INT_MAX bandwidth setting remains in place unless the device
is probed.

> > 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.

Because CONFIG_QCOM_ICC_BWMON is not enabled for the board in question (see
above). It could be enabled as a short term mitigtion, however we shouldn't
require drivers to be enabled just because the DT has a corresponding node.