From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH v3 0/8] NVIDIA Tegra clocksource driver improvements Date: Mon, 3 Jun 2019 14:14:59 +0300 Message-ID: References: <20190524153253.28564-1-digetx@gmail.com> <20190531082634.GA6070@pdeschrijver-desktop.Nvidia.com> <20190603071750.GA29894@pdeschrijver-desktop.Nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190603071750.GA29894@pdeschrijver-desktop.Nvidia.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Peter De Schrijver Cc: Daniel Lezcano , Thomas Gleixner , Joseph Lo , Thierry Reding , Jonathan Hunter , linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, Nicolas Chauvet List-Id: linux-tegra@vger.kernel.org 03.06.2019 10:17, Peter De Schrijver пишет: > On Fri, May 31, 2019 at 03:33:41PM +0300, Dmitry Osipenko wrote: >> 31.05.2019 11:26, Peter De Schrijver пишет: >>> On Fri, May 24, 2019 at 06:32:45PM +0300, Dmitry Osipenko wrote: >>>> Hello, >>>> >>>> This series primarily unifies the driver code across all Tegra SoC >>>> generations. In a result the clocksources are allocated per-CPU on >>>> older Tegra's and have a higher rating than the arch-timer, the newer >>>> Tegra210 is getting support for microsecond clocksource and the driver's >>>> code is getting much cleaner. Note that arch-timer usage is discouraged on >>>> all Tegra's due to the time jitter caused by the CPU frequency scaling. >>> >>> I think the limitations are more as follows: >>> >>> Chip timer suffers cpu dvfs jitter can wakeup from cc7 >>> T20 us-timer No Yes >>> T20 twd timer Yes No? >>> T30 us-timer No Yes >>> T30 twd timer Yes No? >>> T114 us-timer No Yes >>> T114 arch timer No Yes >>> T124 us-timer No Yes >>> T124 arch timer No Yes >>> T210 us-timer No Yes >>> T210 arch timer No No >>> T210 clk_m timer No Yes >>> >>> right? >> >> Doesn't arch timer run off the CPU clock? If yes (that's what I >> assumed), then it should be affected by the DVFS. Otherwise I'll lower >> the clocksource's rating for T114/124/132. >> > > No. It doesn't. This is the big change between A9 and later CPUs. Thank you for the clarification, I'll add a patch to lower the rating where appropriate.