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[91.78.220.99]) by smtp.googlemail.com with ESMTPSA id q21sm12829914lfc.96.2019.08.02.07.26.46 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Aug 2019 07:26:46 -0700 (PDT) Subject: Re: [PATCH v3 1/2] soc/tegra: pmc: Query PCLK clock rate at probe time To: Peter De Schrijver Cc: Thierry Reding , Jonathan Hunter , linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190730174020.15878-1-digetx@gmail.com> <20190802133846.GC3883@pdeschrijver-desktop.Nvidia.com> From: Dmitry Osipenko Message-ID: <218c3d60-1a56-7ee8-840b-7d0559cd8c8e@gmail.com> Date: Fri, 2 Aug 2019 17:26:45 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190802133846.GC3883@pdeschrijver-desktop.Nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 02.08.2019 16:38, Peter De Schrijver пишет: > On Tue, Jul 30, 2019 at 08:40:19PM +0300, Dmitry Osipenko wrote: >> The PCLK clock is running off SCLK, which is a critical clock that is >> very unlikely to randomly change its rate. It is possible to get a >> lockup if kernel decides to enter LP2 cpuidle from a clk-notifier, which >> happens occasionally in a case of Tegra30 EMC driver that waits for the >> clk-change event in the clk-notify handler, because CCF's 'prepare' mutex >> in kept locked and thus clk_get_rate() wants to sleep with interrupts >> being disabled. >> > > I don't think this is the right solution. Eventually we will want to > scale sclk and pclk because the clock tree power of those is not > insignificant. Maybe register a notifier which updates the PMC timer > values when pclk changes? I also had a thought about the notifier for pclk, but wasn't sure if it's really worthwhile right now since there is no real use-case and it's not obvious when such case will materialize. So, I'd say that solution is correct but incomplete. I'll make a v4 with the notifier, since you're asking about it. Thanks for the review!