Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965650AbbKDRVq (ORCPT ); Wed, 4 Nov 2015 12:21:46 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33816 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964910AbbKDRVp (ORCPT ); Wed, 4 Nov 2015 12:21:45 -0500 MIME-Version: 1.0 In-Reply-To: References: Date: Wed, 4 Nov 2015 18:04:55 +0100 Message-ID: Subject: Re: i.MX6: Increasing VPU frequency From: Jon Nettleton To: Jean-Michel Hautbois Cc: linux-kernel , linux-clk@vger.kernel.org, linux-arm-kernel , sboyd@codeaurora.org, mturquette@baylibre.com, Sascha Hauer , Shawn Guo , Fabio Estevam Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1554 Lines: 36 On Wed, Nov 4, 2015 at 5:52 PM, Jean-Michel Hautbois 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. -Jon -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/