diff options
| -rw-r--r-- | drivers/clk/clk.c | 89 |
1 files changed, 44 insertions, 45 deletions
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index 934cfd18f72d..399b0d8ac562 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -1377,23 +1377,33 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent, u8 p_index) unsigned long flags; int ret = 0; struct clk *old_parent = clk->parent; - bool migrated_enable = false; - /* migrate prepare */ - if (clk->prepare_count) + /* + * Migrate prepare state between parents and prevent race with + * clk_enable(). + * + * If the clock is not prepared, then a race with + * clk_enable/disable() is impossible since we already have the + * prepare lock (future calls to clk_enable() need to be preceded by + * a clk_prepare()). + * + * If the clock is prepared, migrate the prepared state to the new + * parent and also protect against a race with clk_enable() by + * forcing the clock and the new parent on. This ensures that all + * future calls to clk_enable() are practically NOPs with respect to + * hardware and software states. + * + * See also: Comment for clk_set_parent() below. + */ + if (clk->prepare_count) { __clk_prepare(parent); - - flags = clk_enable_lock(); - - /* migrate enable */ - if (clk->enable_count) { - __clk_enable(parent); - migrated_enable = true; + clk_enable(parent); + clk_enable(clk); } /* update the clk tree topology */ + flags = clk_enable_lock(); clk_reparent(clk, parent); - clk_enable_unlock(flags); /* change clock input source */ @@ -1401,43 +1411,27 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent, u8 p_index) ret = clk->ops->set_parent(clk->hw, p_index); if (ret) { - /* - * The error handling is tricky due to that we need to release - * the spinlock while issuing the .set_parent callback. This - * means the new parent might have been enabled/disabled in - * between, which must be considered when doing rollback. - */ flags = clk_enable_lock(); - clk_reparent(clk, old_parent); - - if (migrated_enable && clk->enable_count) { - __clk_disable(parent); - } else if (migrated_enable && (clk->enable_count == 0)) { - __clk_disable(old_parent); - } else if (!migrated_enable && clk->enable_count) { - __clk_disable(parent); - __clk_enable(old_parent); - } - clk_enable_unlock(flags); - if (clk->prepare_count) + if (clk->prepare_count) { + clk_disable(clk); + clk_disable(parent); __clk_unprepare(parent); - + } return ret; } - /* clean up enable for old parent if migration was done */ - if (migrated_enable) { - flags = clk_enable_lock(); - __clk_disable(old_parent); - clk_enable_unlock(flags); - } - - /* clean up prepare for old parent if migration was done */ - if (clk->prepare_count) + /* + * Finish the migration of prepare state and undo the changes done + * for preventing a race with clk_enable(). + */ + if (clk->prepare_count) { + clk_disable(clk); + clk_disable(old_parent); __clk_unprepare(old_parent); + } /* update debugfs with new clk tree topology */ clk_debug_reparent(clk, parent); @@ -1449,12 +1443,17 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent, u8 p_index) * @clk: the mux clk whose input we are switching * @parent: the new input to clk * - * Re-parent clk to use parent as it's new input source. If clk has the - * CLK_SET_PARENT_GATE flag set then clk must be gated for this - * operation to succeed. After successfully changing clk's parent - * clk_set_parent will update the clk topology, sysfs topology and - * propagate rate recalculation via __clk_recalc_rates. Returns 0 on - * success, -EERROR otherwise. + * Re-parent clk to use parent as its new input source. If clk is in + * prepared state, the clk will get enabled for the duration of this call. If + * that's not acceptable for a specific clk (Eg: the consumer can't handle + * that, the reparenting is glitchy in hardware, etc), use the + * CLK_SET_PARENT_GATE flag to allow reparenting only when clk is unprepared. + * + * After successfully changing clk's parent clk_set_parent will update the + * clk topology, sysfs topology and propagate rate recalculation via + * __clk_recalc_rates. + * + * Returns 0 on success, -EERROR otherwise. */ int clk_set_parent(struct clk *clk, struct clk *parent) { |