From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Hunter Subject: Re: [PATCH 1/2] cpufreq: tegra186: Fix initial frequency Date: Tue, 14 Jul 2020 08:26:39 +0100 Message-ID: References: <20200712100645.13927-1-jonathanh@nvidia.com> <20200713032554.cykywnygxln6ukrl@vireshk-i7> <3d6091f2-6b04-185f-6c23-e39a34b87877@nvidia.com> <20200714034635.2zdv3wzmftjg2t4a@vireshk-i7> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200714034635.2zdv3wzmftjg2t4a@vireshk-i7> Content-Language: en-US Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Viresh Kumar Cc: Thierry Reding , "Rafael J . Wysocki" , linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org On 14/07/2020 04:46, Viresh Kumar wrote: > On 13-07-20, 17:37, Jon Hunter wrote: >> >> On 13/07/2020 04:25, Viresh Kumar wrote: >>> On 12-07-20, 11:06, Jon Hunter wrote: >>>> Commit 6cc3d0e9a097 ("cpufreq: tegra186: add >>>> CPUFREQ_NEED_INITIAL_FREQ_CHECK flag") fixed CPUFREQ support for >>>> Tegra186 but as a consequence the following warnings are now seen on >>>> boot ... >>>> >>>> cpufreq: cpufreq_online: CPU0: Running at unlisted freq: 0 KHz >>>> cpufreq: cpufreq_online: CPU0: Unlisted initial frequency changed to: 2035200 KHz >>>> cpufreq: cpufreq_online: CPU1: Running at unlisted freq: 0 KHz >>>> cpufreq: cpufreq_online: CPU1: Unlisted initial frequency changed to: 2035200 KHz >>>> cpufreq: cpufreq_online: CPU2: Running at unlisted freq: 0 KHz >>>> cpufreq: cpufreq_online: CPU2: Unlisted initial frequency changed to: 2035200 KHz >>>> cpufreq: cpufreq_online: CPU3: Running at unlisted freq: 0 KHz >>>> cpufreq: cpufreq_online: CPU3: Unlisted initial frequency changed to: 2035200 KHz >>>> cpufreq: cpufreq_online: CPU4: Running at unlisted freq: 0 KHz >>>> cpufreq: cpufreq_online: CPU4: Unlisted initial frequency changed to: 2035200 KHz >>>> cpufreq: cpufreq_online: CPU5: Running at unlisted freq: 0 KHz >>>> cpufreq: cpufreq_online: CPU5: Unlisted initial frequency changed to: 2035200 KHz >>>> >>>> Although we could fix this by adding a 'get' operator for the Tegra186 >>>> CPUFREQ driver, there is really little point because the CPUFREQ on >>>> Tegra186 is set by writing a value stored in the frequency table to a >>>> register and we just need to set the initial frequency. >>> >>> The hardware still runs at the frequency requested by cpufreq core here, right ? >> >> Yes. >> >>> It is better to provide the get() callback as it is also used to show the >>> current frequency in userspace. >> >> I looked at that and I saw that if the get() callback is not provided, >> the current frequency showed by userspace is policy->cur. For this >> device, policy->cur is accurate and so if we added the get() callback we >> essentially just going to return policy->cur. Therefore, given that we >> already know policy->cur, I did not see the point in adding a device >> specific handler to do the same thing. > > The get() callback is supposed to read the frequency from hardware and > return it, no cached value here. policy->cur may end up being wrong in > case there is a bug. OK, I can add a get callback. However, there are a few other drivers that set the current frequency in the init() and don't implement a get() callback ... drivers/cpufreq/pasemi-cpufreq.c drivers/cpufreq/ppc_cbe_cpufreq.c drivers/cpufreq/intel_pstate.c Jon -- nvpublic