Quoting Laurent Pinchart (2013-03-27 02:08:15)
Hi Mike,
Thanks for the patch.
Please see below for a couple of comments.
On Wednesday 27 March 2013 00:09:43 Mike Turquette wrote:
Reentrancy into the clock framework from the clk.h api is necessary for clocks that are prepared and unprepared via i2c_transfer (which includes many PMICs and discrete audio chips) as well as for several other use cases.
This patch implements reentrancy by adding two global atomic_t's which track the context of the current caller. Context in this case is the return value from get_current(). One context variable is for slow operations protected by the prepare_mutex and the other is for fast operations protected by the enable_lock spinlock.
The clk.h api implementations are modified to first see if the relevant global lock is already held and if so compare the global context (set by whoever is holding the lock) against their own context (via a call to get_current()). If the two match then this function is a nested call from the one already holding the lock and we procede. If the context does not match then procede to call mutex_lock and busy-wait for the existing task to complete.
This patch does not increase concurrency for unrelated calls into the clock framework. Instead it simply allows reentrancy by the single task which is currently holding the global clock framework lock.
Signed-off-by: Mike Turquette mturquette@linaro.org Cc: Rajagopal Venkat rajagopal.venkat@linaro.org Cc: David Brown davidb@codeaurora.org Cc: Ulf Hansson ulf.hansson@linaro.org Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com
drivers/clk/clk.c | 255 +++++++++++++++++++++++++++++++++++--------------- 1 file changed, 186 insertions(+), 69 deletions(-)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index 5e8ffff..17432a5 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -19,9 +19,12 @@ #include <linux/of.h> #include <linux/device.h> #include <linux/init.h> +#include <linux/sched.h>
static DEFINE_SPINLOCK(enable_lock); static DEFINE_MUTEX(prepare_lock); +static atomic_t prepare_context; +static atomic_t enable_context;
static HLIST_HEAD(clk_root_list); static HLIST_HEAD(clk_orphan_list);
[snip]
@@ -566,6 +548,35 @@ struct clk *__clk_lookup(const char *name) return NULL; }
+/*** locking & reentrancy ***/
+static void clk_fwk_lock(void) +{
/* hold the framework-wide lock, context == NULL */mutex_lock(&prepare_lock);/* set context for any reentrant calls */atomic_set(&prepare_context, (int) get_current());Won't that break on 64-bit architectures with sizeof(void *) != sizeof(int) ?
Ok, I can use atomic64_t in the next version. Good catch.
I wonder if it would make sense to abstract these operations in a generic recursive mutex. Given that it would delay this patch past v3.10 I won't push for that.
Having a nice implementation of recursive mutexes would have saved me some time.
+}
+static void clk_fwk_unlock(void) +{
/* clear the context */atomic_set(&prepare_context, 0);/* release the framework-wide lock, context == NULL */mutex_unlock(&prepare_lock);+}
+static bool clk_is_reentrant(void) +{
if (mutex_is_locked(&prepare_lock))if ((void *) atomic_read(&prepare_context) == get_current())return true;return false;+}
/*** clk api ***/
void __clk_unprepare(struct clk *clk)
[snip]
@@ -877,6 +945,30 @@ static void __clk_recalc_rates(struct clk *clk, unsigned long msg) __clk_recalc_rates(child, msg); }
+unsigned long __clk_get_rate(struct clk *clk) +{
unsigned long ret;if (!clk) {ret = 0;goto out;You could return 0 directly here.
Call me crazy, but I prefer having a single return statement in a function if possible. That goes for the similar review comments below.
}if (clk->flags & CLK_GET_RATE_NOCACHE)__clk_recalc_rates(clk, 0);ret = clk->rate;if (clk->flags & CLK_IS_ROOT)goto out;And return ret here.
if (!clk->parent)ret = 0;+out:
return ret;+}
/**
- clk_get_rate - return the rate of clk
- @clk: the clk whose rate is being returned
@@ -889,14 +981,22 @@ unsigned long clk_get_rate(struct clk *clk) { unsigned long rate;
mutex_lock(&prepare_lock);
/** FIXME - any locking here seems heavy weight* can clk->rate be replaced with an atomic_t?* same logic can likely be applied to prepare_count & enable_count*/
if (clk && (clk->flags & CLK_GET_RATE_NOCACHE))__clk_recalc_rates(clk, 0);
if (clk_is_reentrant()) {rate = __clk_get_rate(clk);goto out;You can return directly here as well.
}clk_fwk_lock(); rate = __clk_get_rate(clk);
mutex_unlock(&prepare_lock);
clk_fwk_unlock();+out: return rate; } EXPORT_SYMBOL_GPL(clk_get_rate); @@ -1073,6 +1173,39 @@ static void clk_change_rate(struct clk *clk) clk_change_rate(child); }
+int __clk_set_rate(struct clk *clk, unsigned long rate) +{
int ret = 0;struct clk *top, *fail_clk;/* bail early if nothing to do */if (rate == clk->rate)return 0;if ((clk->flags & CLK_SET_RATE_GATE) && clk->prepare_count) {return -EBUSY;}Braces are not necessary.
No harm in having them, but I can remove them in the next version.
Thanks for the review, Mike
/* calculate new rates and get the topmost changed clock */top = clk_calc_new_rates(clk, rate);if (!top)return -EINVAL;/* notify that we are about to change rates */fail_clk = clk_propagate_rate_change(top, PRE_RATE_CHANGE);if (fail_clk) {pr_warn("%s: failed to set %s rate\n", __func__,fail_clk->name);clk_propagate_rate_change(top, ABORT_RATE_CHANGE);return -EBUSY;}/* change the rates */clk_change_rate(top);return ret;+}
/**
- clk_set_rate - specify a new rate for clk
- @clk: the clk whose rate is being changed
-- Regards,
Laurent Pinchart