On Wed, Mar 15, 2017 at 02:03:09PM +0100, Lucas Stach wrote: > Am Sonntag, den 12.03.2017, 19:00 +0000 schrieb Russell King: > > Each Vivante GPU contains a clock divider which can divide the GPU clock > > by 2^n, which can lower the power dissipation from the GPU. It has been > > suggested that the GC600 on Dove is responsible for 20-30% of the power > > dissipation from the SoC, so lowering the GPU clock rate provides a way > > to throttle the power dissiptation, and reduce the temperature when the > > SoC gets hot. > > > > This patch hooks the Etnaviv driver into the kernel's thermal management > > to allow the GPUs to be throttled when necessary, allowing a reduction in > > GPU clock rate from /1 to /64 in power of 2 steps. > > Are those power of 2 steps a hardware limitation, or is it something you > implemented this way to get a smaller number of steps, with a more > meaningful difference in clock speed? > My understanding was that the FSCALE value is just a regular divider > with all steps values in the range of 1-64 being usable. I don't share your understanding. The Vivante GAL kernel driver only ever sets power-of-two values. I have no evidence to support your suggestion. There's evidence that says your understanding is incorrect however. It isn't a divider. A value of 0x40 gives the fastest clock rate, a value of 0x01 gives the slowest. If it were a binary divider, a value of 0x7f would give the slowest rate - so why doesn't Vivante use that in galcore when putting the GPU into idle/lower power - why do they just 0x01. This all leads me to believe that it's not a binary divider, but a set of bits that select the clock from a set of divide-by-two stages, and having more than one bit set is invalid. However, without definitive information from Vivante, we'll never really know. We're unlikely to get that. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
