clk: add clock protection mechanism to clk core

The patch adds clk_core_protect and clk_core_unprotect to the internal
CCF API. These functions allow to set a new constraint along the clock
tree to prevent any change, even indirect, which may result in rate
change or glitch.

Tested-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171201215200.23523-7-jbrunet@baylibre.com

2 files changed, 113 insertions, 7 deletions

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index bbe90babdae4..f69a2176cde1 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -62,6 +62,7 @@ struct clk_core {
         bool                    orphan;
         unsigned int            enable_count;
         unsigned int            prepare_count;
+        unsigned int            protect_count;
         unsigned long           min_rate;
         unsigned long           max_rate;
         unsigned long           accuracy;
@@ -170,6 +171,11 @@ static void clk_enable_unlock(unsigned long flags)
         spin_unlock_irqrestore(&enable_lock, flags);
 }
 
+static bool clk_core_rate_is_protected(struct clk_core *core)
+{
+        return core->protect_count;
+}
+
 static bool clk_core_is_prepared(struct clk_core *core)
 {
         bool ret = false;
@@ -381,6 +387,11 @@ bool clk_hw_is_prepared(const struct clk_hw *hw)
         return clk_core_is_prepared(hw->core);
 }
 
+bool clk_hw_rate_is_protected(const struct clk_hw *hw)
+{
+        return clk_core_rate_is_protected(hw->core);
+}
+
 bool clk_hw_is_enabled(const struct clk_hw *hw)
 {
         return clk_core_is_enabled(hw->core);
@@ -519,6 +530,68 @@ EXPORT_SYMBOL_GPL(__clk_mux_determine_rate_closest);
 
 /***        clk api        ***/
 
+static void clk_core_rate_unprotect(struct clk_core *core)
+{
+        lockdep_assert_held(&prepare_lock);
+
+        if (!core)
+                return;
+
+        if (WARN_ON(core->protect_count == 0))
+                return;
+
+        if (--core->protect_count > 0)
+                return;
+
+        clk_core_rate_unprotect(core->parent);
+}
+
+static int clk_core_rate_nuke_protect(struct clk_core *core)
+{
+        int ret;
+
+        lockdep_assert_held(&prepare_lock);
+
+        if (!core)
+                return -EINVAL;
+
+        if (core->protect_count == 0)
+                return 0;
+
+        ret = core->protect_count;
+        core->protect_count = 1;
+        clk_core_rate_unprotect(core);
+
+        return ret;
+}
+
+static void clk_core_rate_protect(struct clk_core *core)
+{
+        lockdep_assert_held(&prepare_lock);
+
+        if (!core)
+                return;
+
+        if (core->protect_count == 0)
+                clk_core_rate_protect(core->parent);
+
+        core->protect_count++;
+}
+
+static void clk_core_rate_restore_protect(struct clk_core *core, int count)
+{
+        lockdep_assert_held(&prepare_lock);
+
+        if (!core)
+                return;
+
+        if (count == 0)
+                return;
+
+        clk_core_rate_protect(core);
+        core->protect_count = count;
+}
+
 static void clk_core_unprepare(struct clk_core *core)
 {
         lockdep_assert_held(&prepare_lock);
@@ -915,7 +988,9 @@ static int clk_core_determine_round_nolock(struct clk_core *core,
         if (!core)
                 return 0;
 
-        if (core->ops->determine_rate) {
+        if (clk_core_rate_is_protected(core)) {
+                req->rate = core->rate;
+        } else if (core->ops->determine_rate) {
                 return core->ops->determine_rate(core->hw, req);
         } else if (core->ops->round_rate) {
                 rate = core->ops->round_rate(core->hw, req->rate,
@@ -1661,7 +1736,7 @@ static void clk_change_rate(struct clk_core *core)
 static unsigned long clk_core_req_round_rate_nolock(struct clk_core *core,
                                                      unsigned long req_rate)
 {
-        int ret;
+        int ret, cnt;
         struct clk_rate_request req;
 
         lockdep_assert_held(&prepare_lock);
@@ -1669,11 +1744,19 @@ static unsigned long clk_core_req_round_rate_nolock(struct clk_core *core,
         if (!core)
                 return 0;
 
+        /* simulate what the rate would be if it could be freely set */
+        cnt = clk_core_rate_nuke_protect(core);
+        if (cnt < 0)
+                return cnt;
+
         clk_core_get_boundaries(core, &req.min_rate, &req.max_rate);
         req.rate = req_rate;
 
         ret = clk_core_round_rate_nolock(core, &req);
 
+        /* restore the protection */
+        clk_core_rate_restore_protect(core, cnt);
+
         return ret ? 0 : req.rate;
 }
 
@@ -1693,6 +1776,10 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
         if (rate == clk_core_get_rate_nolock(core))
                 return 0;
 
+        /* fail on a direct rate set of a protected provider */
+        if (clk_core_rate_is_protected(core))
+                return -EBUSY;
+
         if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
                 return -EBUSY;
 
@@ -1937,6 +2024,9 @@ static int clk_core_set_parent_nolock(struct clk_core *core,
         if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count)
                 return -EBUSY;
 
+        if (clk_core_rate_is_protected(core))
+                return -EBUSY;
+
         /* try finding the new parent index */
         if (parent) {
                 p_index = clk_fetch_parent_index(core, parent);
@@ -2018,6 +2108,9 @@ static int clk_core_set_phase_nolock(struct clk_core *core, int degrees)
         if (!core)
                 return 0;
 
+        if (clk_core_rate_is_protected(core))
+                return -EBUSY;
+
         trace_clk_set_phase(core, degrees);
 
         if (core->ops->set_phase)
@@ -2148,11 +2241,12 @@ static void clk_summary_show_one(struct seq_file *s, struct clk_core *c,
         if (!c)
                 return;
 
-        seq_printf(s, "%*s%-*s %11d %12d %11lu %10lu %-3d\n",
+        seq_printf(s, "%*s%-*s %11d %12d %12d %11lu %10lu %-3d\n",
                    level * 3 + 1, "",
                    30 - level * 3, c->name,
-                   c->enable_count, c->prepare_count, clk_core_get_rate(c),
-                   clk_core_get_accuracy(c), clk_core_get_phase(c));
+                   c->enable_count, c->prepare_count, c->protect_count,
+                   clk_core_get_rate(c), clk_core_get_accuracy(c),
+                   clk_core_get_phase(c));
 }
 
 static void clk_summary_show_subtree(struct seq_file *s, struct clk_core *c,
@@ -2174,8 +2268,8 @@ static int clk_summary_show(struct seq_file *s, void *data)
         struct clk_core *c;
         struct hlist_head **lists = (struct hlist_head **)s->private;
 
-        seq_puts(s, "   clock                         enable_cnt  prepare_cnt        rate   accuracy   phase\n");
-        seq_puts(s, "----------------------------------------------------------------------------------------\n");
+        seq_puts(s, "   clock                         enable_cnt  prepare_cnt  protect_cnt        rate   accuracy   phase\n");
+        seq_puts(s, "----------------------------------------------------------------------------------------------------\n");
 
         clk_prepare_lock();
 
@@ -2210,6 +2304,7 @@ static void clk_dump_one(struct seq_file *s, struct clk_core *c, int level)
         seq_printf(s, "\"%s\": { ", c->name);
         seq_printf(s, "\"enable_count\": %d,", c->enable_count);
         seq_printf(s, "\"prepare_count\": %d,", c->prepare_count);
+        seq_printf(s, "\"protect_count\": %d,", c->protect_count);
         seq_printf(s, "\"rate\": %lu,", clk_core_get_rate(c));
         seq_printf(s, "\"accuracy\": %lu,", clk_core_get_accuracy(c));
         seq_printf(s, "\"phase\": %d", clk_core_get_phase(c));
@@ -2340,6 +2435,11 @@ static int clk_debug_create_one(struct clk_core *core, struct dentry *pdentry)
         if (!d)
                 goto err_out;
 
+        d = debugfs_create_u32("clk_protect_count", S_IRUGO, core->dentry,
+                        (u32 *)&core->protect_count);
+        if (!d)
+                goto err_out;
+
         d = debugfs_create_u32("clk_notifier_count", S_IRUGO, core->dentry,
                         (u32 *)&core->notifier_count);
         if (!d)
@@ -2911,6 +3011,11 @@ void clk_unregister(struct clk *clk)
         if (clk->core->prepare_count)
                 pr_warn("%s: unregistering prepared clock: %s\n",
                                         __func__, clk->core->name);
+
+        if (clk->core->protect_count)
+                pr_warn("%s: unregistering protected clock: %s\n",
+                                        __func__, clk->core->name);
+
         kref_put(&clk->core->ref, __clk_release);
 unlock:
         clk_prepare_unlock();
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 7c925e6211f1..73ac87f34df9 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -744,6 +744,7 @@ unsigned long clk_hw_get_rate(const struct clk_hw *hw);
 unsigned long __clk_get_flags(struct clk *clk);
 unsigned long clk_hw_get_flags(const struct clk_hw *hw);
 bool clk_hw_is_prepared(const struct clk_hw *hw);
+bool clk_hw_rate_is_protected(const struct clk_hw *hw);
 bool clk_hw_is_enabled(const struct clk_hw *hw);
 bool __clk_is_enabled(struct clk *clk);
 struct clk *__clk_lookup(const char *name);