Rex-BC Chen <rex-bc.chen@xxxxxxxxxxxx> writes: > On Fri, 2022-04-08 at 13:54 -0700, Kevin Hilman wrote: >> Rex-BC Chen <rex-bc.chen@xxxxxxxxxxxx> writes: >> >> > From: Jia-Wei Chang <jia-wei.chang@xxxxxxxxxxxx> >> > >> > In some MediaTek SoCs, like MT8183, CPU and CCI share the same >> > power >> > supplies. Cpufreq needs to check if CCI devfreq exists and wait >> > until >> > CCI devfreq ready before scaling frequency. >> > >> > - Add is_ccifreq_ready() to link CCI device to CPI, and CPU will >> > start >> > DVFS when CCI is ready. >> > - Add platform data for MT8183. >> > >> > Signed-off-by: Jia-Wei Chang <jia-wei.chang@xxxxxxxxxxxx> >> >> The checks here are not enough, and will lead to unexpected behavior. >> IIUC, before doing DVFS, you're checking: >> >> 1) if the "cci" DT node is present and >> 2) if the driver for that device is bound >> >> If both those conditions are not met, you don't actually fail, you >> just >> silently do nothing in ->set_target(). As Angelo pointed out also, >> this >> is not a good idea, and will be rather confusing to users. >> >> The same thing would happen if the cci DT node was present, but the >> CCI >> devfreq driver was disabled. Silent failure would also be quite >> unexpected behavior. Similarily, if the cci DT node is not present >> at >> all (like it is in current upstream DT), this CPUfreq driver will >> silently do nothing. Not good. >> >> So, this patch needs to handle several scenarios: >> >> 1) CCI DT node not present >> >> In this case, the driver should still operate normally. With no CCI >> node, or driver there's no conflict. >> >> 2) CCI DT present/enabled but not yet bound >> >> In this case, you could return -EAGAIN as suggested by Angelo, or >> maybe >> better, it should do a deferred probe. >> >> 3) CCI DT present, but driver disabled >> >> This case is similar to (1), this driver should continue to work. >> >> Kevin > > Hello Kevin and Angelo, > > In my review, if we do not get the link or the link status is not > correct between cci and cpufreq in target_index, I think it will never > established again for this link. > Because it's not checked in probe stage. > > So I think we just need to deal with the issue without cci device, and > don't expect the link between cci and cpufreq will be connected again. > > If I am wrong, please correct me. I don't fully understand your questions, but I think what your getting at suggest that you might need to use deferred probe to handle the case where the ordering of CCI and cpufreq probing is not predictable. Kevin
