From 02ae2bc6febd90cf3de61b6a1bdf491966ed410f Mon Sep 17 00:00:00 2001 From: Chen-Yu Tsai Date: Thu, 13 Apr 2017 10:13:52 +0800 Subject: [PATCH] clk: sunxi-ng: Add clk notifier to gate then ungate PLL clocks In common PLL designs, changes to the dividers take effect almost immediately, while changes to the multipliers (implemented as dividers in the feedback loop) take a few cycles to work into the feedback loop for the PLL to stablize. Sometimes when the PLL clock rate is changed, the decrease in the divider is too much for the decrease in the multiplier to catch up. The PLL clock rate will spike, and in some cases, might lock up completely. This is especially the case if the divider changed is the pre-divider, which affects the reference frequency. This patch introduces a clk notifier callback that will gate and then ungate a clk after a rate change, effectively resetting it, so it continues to work, despite any possible lockups. Care must be taken to reparent any consumers to other temporary clocks during the rate change, and that this notifier callback must be the first to be registered. This is intended to fix occasional lockups with cpufreq on newer Allwinner SoCs, such as the A33 and the H3. Previously it was thought that reparenting the cpu clock away from the PLL while it stabilized was enough, as this worked quite well on the A31. On the A33, hangs have been observed after cpufreq was recently introduced. With the H3, a more thorough test [1] showed that reparenting alone isn't enough. The system still locks up unless the dividers are limited to 1. A hunch was if the PLL was stuck in some unknown state, perhaps gating then ungating it would bring it back to normal. Tests done by Icenowy Zheng using Ondrej's test firmware shows this to be a valid solution. [1] http://www.spinics.net/lists/arm-kernel/msg552501.html Reported-by: Ondrej Jirman Signed-off-by: Chen-Yu Tsai Tested-by: Icenowy Zheng Tested-by: Quentin Schulz Signed-off-by: Maxime Ripard --- drivers/clk/sunxi-ng/ccu_common.c | 49 +++++++++++++++++++++++++++++++ drivers/clk/sunxi-ng/ccu_common.h | 12 ++++++++ 2 files changed, 61 insertions(+) diff --git a/drivers/clk/sunxi-ng/ccu_common.c b/drivers/clk/sunxi-ng/ccu_common.c index 8a47bafd7890..9d8724715a43 100644 --- a/drivers/clk/sunxi-ng/ccu_common.c +++ b/drivers/clk/sunxi-ng/ccu_common.c @@ -14,11 +14,13 @@ * GNU General Public License for more details. */ +#include #include #include #include #include "ccu_common.h" +#include "ccu_gate.h" #include "ccu_reset.h" static DEFINE_SPINLOCK(ccu_lock); @@ -39,6 +41,53 @@ void ccu_helper_wait_for_lock(struct ccu_common *common, u32 lock) WARN_ON(readl_relaxed_poll_timeout(addr, reg, reg & lock, 100, 70000)); } +/* + * This clock notifier is called when the frequency of a PLL clock is + * changed. In common PLL designs, changes to the dividers take effect + * almost immediately, while changes to the multipliers (implemented + * as dividers in the feedback loop) take a few cycles to work into + * the feedback loop for the PLL to stablize. + * + * Sometimes when the PLL clock rate is changed, the decrease in the + * divider is too much for the decrease in the multiplier to catch up. + * The PLL clock rate will spike, and in some cases, might lock up + * completely. + * + * This notifier callback will gate and then ungate the clock, + * effectively resetting it, so it proceeds to work. Care must be + * taken to reparent consumers to other temporary clocks during the + * rate change, and that this notifier callback must be the first + * to be registered. + */ +static int ccu_pll_notifier_cb(struct notifier_block *nb, + unsigned long event, void *data) +{ + struct ccu_pll_nb *pll = to_ccu_pll_nb(nb); + int ret = 0; + + if (event != POST_RATE_CHANGE) + goto out; + + ccu_gate_helper_disable(pll->common, pll->enable); + + ret = ccu_gate_helper_enable(pll->common, pll->enable); + if (ret) + goto out; + + ccu_helper_wait_for_lock(pll->common, pll->lock); + +out: + return notifier_from_errno(ret); +} + +int ccu_pll_notifier_register(struct ccu_pll_nb *pll_nb) +{ + pll_nb->clk_nb.notifier_call = ccu_pll_notifier_cb; + + return clk_notifier_register(pll_nb->common->hw.clk, + &pll_nb->clk_nb); +} + int sunxi_ccu_probe(struct device_node *node, void __iomem *reg, const struct sunxi_ccu_desc *desc) { diff --git a/drivers/clk/sunxi-ng/ccu_common.h b/drivers/clk/sunxi-ng/ccu_common.h index 73d81dc58fc5..d6fdd7a789aa 100644 --- a/drivers/clk/sunxi-ng/ccu_common.h +++ b/drivers/clk/sunxi-ng/ccu_common.h @@ -83,6 +83,18 @@ struct sunxi_ccu_desc { void ccu_helper_wait_for_lock(struct ccu_common *common, u32 lock); +struct ccu_pll_nb { + struct notifier_block clk_nb; + struct ccu_common *common; + + u32 enable; + u32 lock; +}; + +#define to_ccu_pll_nb(_nb) container_of(_nb, struct ccu_pll_nb, clk_nb) + +int ccu_pll_notifier_register(struct ccu_pll_nb *pll_nb); + int sunxi_ccu_probe(struct device_node *node, void __iomem *reg, const struct sunxi_ccu_desc *desc); -- 2.20.1