Am Mittwoch, den 15.03.2017, 14:05 +0000 schrieb Russell King - ARM Linux: > 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. > Yes, it seems your understanding is correct and my mental model of this FSCALE thing was off. I'll pick up this patch for the next round of etnaviv features. Regards, Lucas _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
