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Set an appropriate limit on the maximum scal= ing > > > > > frequency. > > > > > > > > Looking at downstream, from what I can tell, the CPU's maximum freq= uency is indeed 1.55GHz under normal conditions. However, at temperatures o= ver 90C, its voltage is limited to 1090mV. Reference: > > > > > > > > static struct dvfs_therm_limits > > > > tegra210_core_therm_caps_ucm2[MAX_THERMAL_LIMITS] =3D { > > > > {86, 1090}, > > > > {0, 0}, > > > > }; > > > > (rel-32 kernel-4.9/drivers/soc/tegra/tegra210-dvfs.c) > > > > > > > > Here the throttling is set at 86C, I suppose to give some margin. > > > > > > > > 1090mV perfectly matches the 1.479GHz operating point defined in th= e upstream kernel. So it seems to me that rather than setting a maximum fre= quency, we would need temperature dependent DVFS. Or, at least as a first s= tep, we could have the driver just always limit the maximum frequency so it= fits under the thermal cap voltage -- the temperature limit is rather high= , after all. > > > > > > > > If you have other information, please do tell. > > > > > > I am basing on this line in the downstream porg dt repo: > > > > > > nvidia,dfll-max-freq-khz =3D <1479000>; > > > (tegra-l4t-r32.7.6_good kernel-dts/tegra210-porg-p3448-common.dtsi) > > > > > > Which in the downstream dfll driver limits the max frequency it will = use: > > > > > > max_freq =3D fcpu_data->cpu_max_freq_table[speedo_id]; > > > if (!of_property_read_u32(pdev->dev.of_node, "nvidia,dfll-max= -freq-khz", > > > &f)) > > > max_freq =3D min(max_freq, f * 1000UL); > > > (tegra-l4t-r32.7.6_good drivers/clk/tegra/clk-tegra124-dfll-fcpu.c) > > > > > > If I read the commit history correctly, it does appear that this limi= t > > > was set because the always-on use case was failing thermal tests. I > > > couldn't say if it was intentional that this throttling was applied t= o > > > all use cases or not, but that is what appears to have happened. Henc= e > > > trying to replicate here in an effort to squash stability issues. > > > > I can't see any reference to failing thermal tests. Can to point to the= commit? >=20 > In the porg dt repo, commit hash d1326f08, which adds the > nvidia,dfll-max-freq-khz property, the message body states: "Set > CPU/GPU Fmax limit for 24x7 105C UCM." I read that to mean that the > 24x7 always-on use case model was failing to stay under 105C unless > the cpu and gpu frequencies were limited. Is that an incorrect > reading? 105C is kind of a crazy number anyways, beyond the soctherm > critical shutdown temperature. What that's (trying) to say is that it sets the CPU's Fmax to the limit spe= cified by the 24x7 105C UCM profile, which is the 1090mV i.e. 1.4GHz limit.= The profile is called that because it's normally used for the 90C-105C tem= perature range. >=20 > > I looked into why this was added for porg -- it does not seem to be rel= ated to reliability, but more so consistency of performance. I don't think = that's a huge concern for upstream -- though in any case we should be cappi= ng the frequency in the DFLL driver for now since we don't support dynamic = thermal capping. >=20 > So the whole conversation winds around to: The change is valid, but > the commit message needs better justification? In my opinion, there is no need to add the device tree property in upstream= . The CPU is designed to work at 1.5GHz under 90C, and 1.4GHz between 90C t= o 105C. I think this is a bit of a downstream-ism and not something we shou= ld add in upstream. If the user wants to underclock, then that should be th= rough the cpufreq governor or such mechanism. >=20 > As a side note: I'm still chasing multiple stability issues on various > t210 devices. Though, the only one I've seen on p3450/p3541 is that > nouveau intermittently fails to init the gpu. Just hangs on probe and > eventually something times out, stack traces, and causes a panic > reboot. Seems to be about a 50/50 chance for me, but works fine if > probe succeeds. For another dev, it only works once in a blue moon, > but still dies shortly thereafter even if probe works. I thought it > might be related to the cpu/gpu getting 'overclocked'. But even after > this series, the problem persists. So maybe me calling this underclock > a stability fix is inaccurate. But stability issues still exist. Good to know. It doesn't strike me as a CPU issue -- I'd put the first plac= e to look at nouveau's init code itself to see what is failing. There's a l= ot of potential software issues that can cause intermittencies during GPU b= oot. If power related, GPU or SOC rail. Thanks, Mikko >=20 > Aaron