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Set an appropriate limit on the maximum scaling > > > frequency. > > > > Looking at downstream, from what I can tell, the CPU's maximum frequenc= y is indeed 1.55GHz under normal conditions. However, at temperatures over = 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 the up= stream kernel. So it seems to me that rather than setting a maximum frequen= cy, we would need temperature dependent DVFS. Or, at least as a first step,= we could have the driver just always limit the maximum frequency so it fit= s under the thermal cap voltage -- the temperature limit is rather high, af= ter all. > > > > If you have other information, please do tell. >=20 > I am basing on this line in the downstream porg dt repo: >=20 > nvidia,dfll-max-freq-khz =3D <1479000>; > (tegra-l4t-r32.7.6_good kernel-dts/tegra210-porg-p3448-common.dtsi) >=20 > Which in the downstream dfll driver limits the max frequency it will use: >=20 > max_freq =3D fcpu_data->cpu_max_freq_table[speedo_id]; > if (!of_property_read_u32(pdev->dev.of_node, "nvidia,dfll-max-fre= q-khz", > &f)) > max_freq =3D min(max_freq, f * 1000UL); > (tegra-l4t-r32.7.6_good drivers/clk/tegra/clk-tegra124-dfll-fcpu.c) >=20 > If I read the commit history correctly, it does appear that this limit > 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 to > all use cases or not, but that is what appears to have happened. Hence > 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 com= mit? I looked into why this was added for porg -- it does not seem to be related= 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 capping t= he frequency in the DFLL driver for now since we don't support dynamic ther= mal capping. >=20 > > Incidentally, some of the CVB tables in the upstream kernel seem to ign= ore speedo (I assume they are conservative) while rel-32 has different tabl= es. So the upstream kernel is probably running at slightly unnecessarily hi= gh voltages. >=20 > This is worrying as well, though most of those tables cannot currently > be used as the fuse driver never assigns those cpu speedo ids. All I > checked in this series was that the correct cpu speedo id was picked > and the appropriate CVB table was applied to p2371-2180, p3450-0000, > and p3541-0000. I haven't yet researched what the speedo values mean > and do. There's many other sku's missing as well. Such as the one's > used by the shield tv's. I have as of yet been unable to boot to > userspace on p2571-0930/1 or p2894-0050, so I haven't determined which > sku(s) are used by those to add them here. I'm in the process of > getting uart access to continue that endeavour. The speedo values are coefficients used to calculate voltage requirements f= or frequency operating points. Usually that kind of stuff starts with conse= rvative constant values that are then refined, so my assumption is that the= fixed values we currently have are safe but unoptimal (at least when they = get used). >=20 > Aaron