[PATCHv3 3/7] clk: mvebu: extend clk-cpu for dynamic frequency scaling

Thomas Petazzoni
2014-07-23T23:54:03Z

+static int clk_cpu_on_set_rate(struct clk_hw *hwclk, unsigned long rate,
+ unsigned long parent_rate)
+{
+ u32 reg;
+ unsigned long fabric_div, target_div, cur_rate;
+ struct cpu_clk *cpuclk = to_cpu_clk(hwclk);
+
+ /*
+ * PMU DFS registers are not mapped, Device Tree does not
+ * describes them. We cannot change the frequency dynamically.
+ */
+ if (!cpuclk->pmu_dfs)
+ return -ENODEV;
+
+ cur_rate = __clk_get_rate(hwclk->clk);
+
+ reg = readl(cpuclk->reg_base + SYS_CTRL_CLK_DIVIDER_CTRL2_OFFSET);
+ fabric_div = (reg >> SYS_CTRL_CLK_DIVIDER_CTRL2_NBCLK_RATIO_SHIFT) &
+ SYS_CTRL_CLK_DIVIDER_MASK;
+
+ /* Frequency is going up */
+ if (rate == 2 * cur_rate)
+ target_div = fabric_div / 2;
+ /* Frequency is going down */
+ else
+ target_div = fabric_div;
+
+ if (target_div == 0)
+ target_div = 1;
+
+ reg = readl(cpuclk->pmu_dfs);
+ reg &= ~(PMU_DFS_RATIO_MASK << PMU_DFS_RATIO_SHIFT);
+ reg |= (target_div << PMU_DFS_RATIO_SHIFT);
+ writel(reg, cpuclk->pmu_dfs);
+
+ reg = readl(cpuclk->reg_base + SYS_CTRL_CLK_DIVIDER_CTRL_OFFSET);
+ reg |= (SYS_CTRL_CLK_DIVIDER_CTRL_RESET_ALL <<
+ SYS_CTRL_CLK_DIVIDER_CTRL_RESET_SHIFT);
+ writel(reg, cpuclk->reg_base + SYS_CTRL_CLK_DIVIDER_CTRL_OFFSET);
+
+ return mvebu_pmsu_dfs_request(cpuclk->cpu);
+}
+
+static int clk_cpu_set_rate(struct clk_hw *hwclk, unsigned long rate,
+ unsigned long parent_rate)
+{
+ if (__clk_is_enabled(hwclk->clk))
+ return clk_cpu_on_set_rate(hwclk, rate, parent_rate);
+ else
+ return clk_cpu_off_set_rate(hwclk, rate, parent_rate);

This is racy. You don't hold the clk_enable lock so it could be enable
between the conditional check and executing clk_cpu_on_set_rate.

How do you ensure that secondary CPU clocks are not enabled/disabled
when changing rates?

Regards,
Mike