On Wed, Nov 4, 2015 at 8:33 PM, Jean-Michel Hautbois <jean-michel.hautb...@veo-labs.com> wrote: > 2015-11-04 18:04 GMT+01:00 Jon Nettleton <jon.nettle...@gmail.com>: >> On Wed, Nov 4, 2015 at 5:52 PM, Jean-Michel Hautbois >> <jean-michel.hautb...@veo-labs.com> wrote: >>> Hi ! >>> >>> I can see in FSL kernel that VPU is configurable to 352M (it defaults >>> at 264MHz in mainline I think). >>> In the TRM, it is even specified at 352MHz as a default frequency, >>> with a maximum of 540MHz. >>> >>> Would it be possible to allow this clock rating modification if, for >>> instance, we select a performance governor in cpufreq, or if a coda >>> encoder is started with 1080p for instance ? >>> If so, then how is it doable properly ? >> >> For some reason the FSL kernel configures the VPU to run at 352Mhz in >> a very odd way that requires limiting the min cpu-frequency to 792Mhz. >> It also requires clocking down a bunch of devices on pll2_pfd2_396m to >> 352Mhz. >> >> The simple solution to this is to instead parent the VPU to >> pll2_pfd0_352m which is unused. I have found by default it is stable >> decoding but unstable encoding at 352Mhz, most likely due to the >> voltage changes needed that limiting the min cpu-freq to 792Mhz >> provides. However everything seems to work quite reliably clocking >> that pfd to 327Mhz, which still gives a boost of almost 24% >> >> In my testing the performance gain in then going from 327 to 352 is >> minimal. Generally I think you hit AXI bus limitations rather than >> VPU performance. > > Interesting. > So you propose to add something like the following in > drivers/clk/imx/clk-imx6q.cdrivers/clk/imx/clk-imx6q.c : > imx_clk_set_rate(clk[IMX6QDL_CLK_PLL2_PFD0_352M], 327000000); > imx_clk_set_parent(clk[IMX6QDL_CLK_VPU_AXI_SEL], > clk[IMX6QDL_CLK_PLL2_PFD0_352M]); > > This should end up with a fastest VPU (in fact ~25% boost is good). > Is it the correct way to do it ? > Should it be done in coda instead ? And only when needed ?
That is how I have done it. I was going to implement dvfs for the vpu but found that this change really added minimal power and thermal overhead. Without looking it up I believe I only saw a 10-20mA rise in power usage and virtually no thermal differences. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/