On Thu, Sep 06, 2018 at 01:39:43PM +0200, Philipp Rossak wrote: > On 06.09.2018 09:24, Quentin Schulz wrote: > > Hi Philipp, > > > > On Thu, Aug 30, 2018 at 05:45:18PM +0200, Philipp Rossak wrote: > > > Since we have now thermal trotteling enabeled we can now add the full > > > range of the OPP table. > > > > > That's not the reason why they were not added. > > > > Please see commit 2db639d8c1663d7543c9ab5323383d94c8a76c63[1]. > > > > Basically, you only want the OPPs which can work below or at the default > > voltage of the CPU supply, because the CPU supply is specific to each > > board. > > > > If you set your CPU to work at a given frequency and the voltage isn't > > updated (saying opp-microvolt = <x>; in DT isn't enough, you need > > cpu-supply to be provided and functional), the CPU might just crash. > > > > Without cpu-supply property, underclocking isn't effective in term of > > thermal cooling or power saving. Overclocking is very, very, very likely > > to make the CPU crash. > > > > It's not a very difficult thing to do to test if a given frequency work > > well but it needs a specific test environment and it's a lengthy test, > > you can have a look at those tools here[3] if you like. It's not because > > it works in a given test case that'll work on the long term under heavy > > load and constant frequency changes. > > > > For A83T, I already did it and the outcome is the patch in [1]. Same for > > A33. > > > > So, if you want to use these three higher OPPs, you need to define them > > in your board DTS and add the cpu-supply property. See what's done for > > the A33 and more specifically the Sinlinx SinA33[2] as an example. > > > > [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2db639d8c1663d7543c9ab5323383d94c8a76c63 > > [2]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun8i-a33-sinlinx-sina33.dts > > [3]http://linux-sunxi.org/Hardware_Reliability_Tests#CPU > > > > Quentin > > > > Hey Quentin, > > thanks for your feedback! > > Sounds like we will never be able to run the A83T on its maximum frequency > in mainline. > > I will do some testing, during the next weeks/months when I have time. > With the old Allwinner kernel I was able to run the A83T with its maximum > frequency without any problems since my board is very good cooled. You definitely can, but I think Quentin's point was to do it on a per-board basis, not for all of the A83t boards at once. Maxime -- Maxime Ripard, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
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