[alsa-devel] [PATCH v2 1/2] ASoC: kirkwood: clk: probe defer when clock not yet ready
At probe time, a clock device may not be ready when some other device wants to use it.
This patch lets the functions clk_get/devm_clk_get return a probe defer when the clock is defined in the DT but not yet available.
Signed-off-by: Jean-Francois Moine moinejf@free.fr --- drivers/clk/clk.c | 2 +- drivers/clk/clkdev.c | 9 +++++++-- 2 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index a004769..582abc8 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -2181,7 +2181,7 @@ EXPORT_SYMBOL_GPL(of_clk_del_provider); struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec) { struct of_clk_provider *provider; - struct clk *clk = ERR_PTR(-ENOENT); + struct clk *clk = ERR_PTR(-EPROBE_DEFER);
/* Check if we have such a provider in our array */ mutex_lock(&of_clk_lock); diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c index 442a313..f8b28d9 100644 --- a/drivers/clk/clkdev.c +++ b/drivers/clk/clkdev.c @@ -157,8 +157,13 @@ struct clk *clk_get(struct device *dev, const char *con_id)
if (dev) { clk = of_clk_get_by_name(dev->of_node, con_id); - if (!IS_ERR(clk) && __clk_get(clk)) - return clk; + if (!IS_ERR(clk)) { + if (__clk_get(clk)) + return clk; + } else { + if (PTR_ERR(clk) == -EPROBE_DEFER) + return clk; + } }
return clk_get_sys(dev_id, con_id);
On Sat, Sep 21, 2013 at 12:00:06PM +0200, Jean-Francois Moine wrote:
diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c index 442a313..f8b28d9 100644 --- a/drivers/clk/clkdev.c +++ b/drivers/clk/clkdev.c @@ -157,8 +157,13 @@ struct clk *clk_get(struct device *dev, const char *con_id)
if (dev) { clk = of_clk_get_by_name(dev->of_node, con_id);
if (!IS_ERR(clk) && __clk_get(clk))return clk;
if (!IS_ERR(clk)) {if (__clk_get(clk))return clk;} else {if (PTR_ERR(clk) == -EPROBE_DEFER)return clk;}
Thanks for patching this file and bringing this code to my attention. The original is fscked. Calling __clk_get() outside of any lock is a serious bug and leads to races.
Also, a failing __clk_get() probably should not drop through to clk_get_sys(), but should instead do this:
if (!IS_ERR(clk)) { if (!__clk_get(clk)) clk = ERR_PTR(-ENOENT); return clk; }
since a _found_ clock but one which can't be used (due to the module going away) is not a reason to drop through to clk_get_sys().
Which means your change should look like this:
if (!IS_ERR(clk)) { if (!__clk_get(clk)) clk = ERR_PTR(-ENOENT); return clk; } if (PTR_ERR(clk) == -EPROBE_DEFER) return clk;
On Sat, Sep 21, 2013 at 12:00:06PM +0200, Jean-Francois Moine wrote:
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index a004769..582abc8 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -2181,7 +2181,7 @@ EXPORT_SYMBOL_GPL(of_clk_del_provider); struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec) { struct of_clk_provider *provider;
- struct clk *clk = ERR_PTR(-ENOENT);
struct clk *clk = ERR_PTR(-EPROBE_DEFER);
/* Check if we have such a provider in our array */ mutex_lock(&of_clk_lock);
diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c index 442a313..f8b28d9 100644 --- a/drivers/clk/clkdev.c +++ b/drivers/clk/clkdev.c @@ -157,8 +157,13 @@ struct clk *clk_get(struct device *dev, const char *con_id)
if (dev) { clk = of_clk_get_by_name(dev->of_node, con_id);
if (!IS_ERR(clk) && __clk_get(clk))return clk;
if (!IS_ERR(clk)) {if (__clk_get(clk))return clk;} else {if (PTR_ERR(clk) == -EPROBE_DEFER)return clk;}
Another comment. This is broken - it will never fall through if a 'dev' is given, because of_clk_get_by_name() will always return an -EPROBE_DEFER error pointer in that case.
So this approach is unworkable.
On Sat, Sep 21, 2013 at 11:47:34AM +0100, Russell King - ARM Linux wrote:
Another comment. This is broken - it will never fall through if a 'dev' is given, because of_clk_get_by_name() will always return an -EPROBE_DEFER error pointer in that case.
So this approach is unworkable.
And another comment:
This whole approach is broken - while Mark is correct that we should find a way to return -EPROBE_DEFER if a clock is specified, the solution here does not allow that - it will return -EPROBE_DEFER whenever the clock is not found _or_ is not specified.
This has the effect of making the external clock *non*optional for the kirkwood-i2s driver, which is also completely broken.
On Sat, 21 Sep 2013 11:47:34 +0100 Russell King - ARM Linux linux@arm.linux.org.uk wrote:
On Sat, Sep 21, 2013 at 12:00:06PM +0200, Jean-Francois Moine wrote:
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index a004769..582abc8 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -2181,7 +2181,7 @@ EXPORT_SYMBOL_GPL(of_clk_del_provider); struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec) { struct of_clk_provider *provider;
- struct clk *clk = ERR_PTR(-ENOENT);
struct clk *clk = ERR_PTR(-EPROBE_DEFER);
/* Check if we have such a provider in our array */ mutex_lock(&of_clk_lock);
diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c index 442a313..f8b28d9 100644 --- a/drivers/clk/clkdev.c +++ b/drivers/clk/clkdev.c @@ -157,8 +157,13 @@ struct clk *clk_get(struct device *dev, const char *con_id)
if (dev) { clk = of_clk_get_by_name(dev->of_node, con_id);
if (!IS_ERR(clk) && __clk_get(clk))return clk;
if (!IS_ERR(clk)) {if (__clk_get(clk))return clk;} else {if (PTR_ERR(clk) == -EPROBE_DEFER)return clk;}Another comment. This is broken - it will never fall through if a 'dev' is given, because of_clk_get_by_name() will always return an -EPROBE_DEFER error pointer in that case.
So this approach is unworkable.
And another comment:
This whole approach is broken - while Mark is correct that we should find a way to return -EPROBE_DEFER if a clock is specified, the solution here does not allow that - it will return -EPROBE_DEFER whenever the clock is not found _or_ is not specified.
This has the effect of making the external clock *non*optional for the kirkwood-i2s driver, which is also completely broken.
It works fine for me (I tried both cases, with and without the external clock).
The scheme is as follows:
- kirkwood-i2s kirkwood_i2s_dev_probe() calls:
priv->extclk = &pdev->dev, "extclk");
- devm_clk_get() calls:
clk = clk_get(dev, id);
- clk_get() does:
if (dev) // this is the case clk = of_clk_get_by_name(dev->of_node, con_id);
- of_clk_get_by_name() does:
if (name) // this is the case index = of_property_match_string(np, "clock-names", name);
Here, if the external clock is declared in the DT, index is >= 0. If there is no externel clock in the DT, index is < 0.
clk = of_clk_get(np, index); if (!IS_ERR(clk)) break; else if (name && index >= 0) { pr_err("ERROR: could not get clock %s:%s(%i)\n", np->full_name, name ? name : "", index); return clk; }
- If the index is < 0, of_clk_get() immediately returns -EINVAL.
So, kirkwood-i2s knows there is no external clock. DONE.
- otherwise, if the index is >= 0 (the external clock is declared in the DT), of_clk_get() gets the phandle (of_parse_phandle_with_args()) and gets the clock (of_clk_get_from_provider()).
This last function returns either the clock (device initialized), a -EPROBE_DEFER error (clock not yet initialized) or some other error (bad DT or clock error).
So, kirkwood-i2s knows there is a declared external clock and it acts according to the return code (accept, defer or ignore). DONE.
Did I miss something?
participants (2)
-
Jean-Francois Moine -
Russell King - ARM Linux