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[91.78.208.152]) by smtp.googlemail.com with ESMTPSA id k3sm8527148lji.43.2020.04.05.07.05.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 05 Apr 2020 07:05:15 -0700 (PDT) Subject: Re: [TEGRA194_CPUFREQ Patch v2 2/3] cpufreq: Add Tegra194 cpufreq driver To: Sumit Gupta , rjw@rjwysocki.net, viresh.kumar@linaro.org, catalin.marinas@arm.com, will@kernel.org, thierry.reding@gmail.com, jonathanh@nvidia.com, talho@nvidia.com, linux-pm@vger.kernel.org, linux-tegra@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: bbasu@nvidia.com, mperttunen@nvidia.com References: <1586028547-14993-1-git-send-email-sumitg@nvidia.com> <1586028547-14993-3-git-send-email-sumitg@nvidia.com> From: Dmitry Osipenko Message-ID: <67f9feb1-ba51-f1ac-b6eb-4587924d0748@gmail.com> Date: Sun, 5 Apr 2020 17:05:14 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <1586028547-14993-3-git-send-email-sumitg@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 04.04.2020 22:29, Sumit Gupta пишет: ... > +static void tegra_read_counters(struct work_struct *work) > +{ > + struct read_counters_work *read_counters_work; > + struct tegra_cpu_ctr *c; > + u64 val; > + > + /* > + * ref_clk_counter(32 bit counter) runs on constant clk, > + * pll_p(408MHz). > + * It will take = 2 ^ 32 / 408 MHz to overflow ref clk counter > + * = 10526880 usec = 10.527 sec to overflow > + * > + * Like wise core_clk_counter(32 bit counter) runs on core clock. > + * It's synchronized to crab_clk (cpu_crab_clk) which runs at > + * freq of cluster. Assuming max cluster clock ~2000MHz, > + * It will take = 2 ^ 32 / 2000 MHz to overflow core clk counter > + * = ~2.147 sec to overflow > + */ > + read_counters_work = container_of(work, struct read_counters_work, > + work); > + c = &read_counters_work->c; > + > + val = read_freq_feedback(); > + c->last_refclk_cnt = lower_32_bits(val); > + c->last_coreclk_cnt = upper_32_bits(val); > + udelay(c->delay); > + val = read_freq_feedback(); > + c->refclk_cnt = lower_32_bits(val); > + c->coreclk_cnt = upper_32_bits(val); > +} > + > +/* > + * Return instantaneous cpu speed > + * Instantaneous freq is calculated as - > + * -Takes sample on every query of getting the freq. > + * - Read core and ref clock counters; > + * - Delay for X us > + * - Read above cycle counters again > + * - Calculates freq by subtracting current and previous counters > + * divided by the delay time or eqv. of ref_clk_counter in delta time > + * - Return Kcycles/second, freq in KHz > + * > + * delta time period = x sec > + * = delta ref_clk_counter / (408 * 10^6) sec > + * freq in Hz = cycles/sec > + * = (delta cycles / x sec > + * = (delta cycles * 408 * 10^6) / delta ref_clk_counter > + * in KHz = (delta cycles * 408 * 10^3) / delta ref_clk_counter > + * > + * @cpu - logical cpu whose freq to be updated > + * Returns freq in KHz on success, 0 if cpu is offline I don't see any checks in the code about whether CPU is offline. Googling for "queue_work_on offline cpu" suggests that this function should hang. > + */ > +static unsigned int tegra194_get_speed_common(u32 cpu, u32 delay) > +{ > + struct read_counters_work read_counters_work; > + struct tegra_cpu_ctr c; > + u32 delta_refcnt; > + u32 delta_ccnt; > + u32 rate_mhz; > + > + read_counters_work.c.cpu = cpu; > + read_counters_work.c.delay = delay; > + INIT_WORK_ONSTACK(&read_counters_work.work, tegra_read_counters); > + queue_work_on(cpu, read_counters_wq, &read_counters_work.work); > + flush_work(&read_counters_work.work); > + c = read_counters_work.c; > + > + if (c.coreclk_cnt < c.last_coreclk_cnt) > + delta_ccnt = c.coreclk_cnt + (MAX_CNT - c.last_coreclk_cnt); > + else > + delta_ccnt = c.coreclk_cnt - c.last_coreclk_cnt; > + if (!delta_ccnt) > + return 0; > + > + /* ref clock is 32 bits */ > + if (c.refclk_cnt < c.last_refclk_cnt) > + delta_refcnt = c.refclk_cnt + (MAX_CNT - c.last_refclk_cnt); > + else > + delta_refcnt = c.refclk_cnt - c.last_refclk_cnt; > + if (!delta_refcnt) { > + pr_debug("cpufreq: %d is idle, delta_refcnt: 0\n", cpu); > + return 0; > + } > + rate_mhz = ((unsigned long)(delta_ccnt * REF_CLK_MHZ)) / delta_refcnt; > + > + return (rate_mhz * KHZ); /* in KHz */ > +}