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

[Matthias Kaehlcke <mka@chromium.org>]

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@quicinc.com>
> >> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.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.