From de61608acf89779c8831aaa1428b6975d49d98c0 Mon Sep 17 00:00:00 2001 From: Lars-Peter Clausen Date: Fri, 19 Apr 2013 11:42:14 +0200 Subject: [PATCH] dma:of: Use a mutex to protect the of_dma_list Currently the OF DMA code uses a spin lock to protect the of_dma_list from concurrent access and a per controller reference count to protect the controller from being freed while a request operation is in progress. If of_dma_controller_free() is called for a controller who's reference count is not zero it will return -EBUSY and not remove the controller. This is fine up until here, but leaves the question what the caller of of_dma_controller_free() is supposed to do if the controller couldn't be freed. The only viable solution for the caller is to spin on of_dma_controller_free() until it returns success. E.g. do { ret = of_dma_controller_free(dev->of_node) } while (ret != -EBUSY); This is rather ugly and unnecessary and none of the current users of of_dma_controller_free() check it's return value anyway. Instead protect the list by a mutex. The mutex will be held as long as a request operation is in progress. So if of_dma_controller_free() is called while a request operation is in progress it will be put to sleep and only wake up once the request operation has finished. This means that it is no longer possible to register or unregister OF DMA controllers from a context where it's not possible to sleep. But I doubt that we'll ever need this. Also rename of_dma_get_controller back to of_dma_find_controller. Signed-off-by: Lars-Peter Clausen Acked-by: Arnd Bergmann Signed-off-by: Vinod Koul --- drivers/dma/of-dma.c | 76 +++++++++++++------------------------------------- include/linux/of_dma.h | 6 ++-- 2 files changed, 22 insertions(+), 60 deletions(-) diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c index 2882403..7aa0864 100644 --- a/drivers/dma/of-dma.c +++ b/drivers/dma/of-dma.c @@ -13,38 +13,31 @@ #include #include #include -#include +#include #include #include #include static LIST_HEAD(of_dma_list); -static DEFINE_SPINLOCK(of_dma_lock); +static DEFINE_MUTEX(of_dma_lock); /** - * of_dma_get_controller - Get a DMA controller in DT DMA helpers list + * of_dma_find_controller - Get a DMA controller in DT DMA helpers list * @dma_spec: pointer to DMA specifier as found in the device tree * * Finds a DMA controller with matching device node and number for dma cells - * in a list of registered DMA controllers. If a match is found the use_count - * variable is increased and a valid pointer to the DMA data stored is retuned. - * A NULL pointer is returned if no match is found. + * in a list of registered DMA controllers. If a match is found a valid pointer + * to the DMA data stored is retuned. A NULL pointer is returned if no match is + * found. */ -static struct of_dma *of_dma_get_controller(struct of_phandle_args *dma_spec) +static struct of_dma *of_dma_find_controller(struct of_phandle_args *dma_spec) { struct of_dma *ofdma; - spin_lock(&of_dma_lock); - list_for_each_entry(ofdma, &of_dma_list, of_dma_controllers) if ((ofdma->of_node == dma_spec->np) && - (ofdma->of_dma_nbcells == dma_spec->args_count)) { - ofdma->use_count++; - spin_unlock(&of_dma_lock); + (ofdma->of_dma_nbcells == dma_spec->args_count)) return ofdma; - } - - spin_unlock(&of_dma_lock); pr_debug("%s: can't find DMA controller %s\n", __func__, dma_spec->np->full_name); @@ -53,22 +46,6 @@ static struct of_dma *of_dma_get_controller(struct of_phandle_args *dma_spec) } /** - * of_dma_put_controller - Decrement use count for a registered DMA controller - * @of_dma: pointer to DMA controller data - * - * Decrements the use_count variable in the DMA data structure. This function - * should be called only when a valid pointer is returned from - * of_dma_get_controller() and no further accesses to data referenced by that - * pointer are needed. - */ -static void of_dma_put_controller(struct of_dma *ofdma) -{ - spin_lock(&of_dma_lock); - ofdma->use_count--; - spin_unlock(&of_dma_lock); -} - -/** * of_dma_controller_register - Register a DMA controller to DT DMA helpers * @np: device node of DMA controller * @of_dma_xlate: translation function which converts a phandle @@ -114,12 +91,11 @@ int of_dma_controller_register(struct device_node *np, ofdma->of_dma_nbcells = nbcells; ofdma->of_dma_xlate = of_dma_xlate; ofdma->of_dma_data = data; - ofdma->use_count = 0; /* Now queue of_dma controller structure in list */ - spin_lock(&of_dma_lock); + mutex_lock(&of_dma_lock); list_add_tail(&ofdma->of_dma_controllers, &of_dma_list); - spin_unlock(&of_dma_lock); + mutex_unlock(&of_dma_lock); return 0; } @@ -131,32 +107,20 @@ EXPORT_SYMBOL_GPL(of_dma_controller_register); * * Memory allocated by of_dma_controller_register() is freed here. */ -int of_dma_controller_free(struct device_node *np) +void of_dma_controller_free(struct device_node *np) { struct of_dma *ofdma; - spin_lock(&of_dma_lock); - - if (list_empty(&of_dma_list)) { - spin_unlock(&of_dma_lock); - return -ENODEV; - } + mutex_lock(&of_dma_lock); list_for_each_entry(ofdma, &of_dma_list, of_dma_controllers) if (ofdma->of_node == np) { - if (ofdma->use_count) { - spin_unlock(&of_dma_lock); - return -EBUSY; - } - list_del(&ofdma->of_dma_controllers); - spin_unlock(&of_dma_lock); kfree(ofdma); - return 0; + break; } - spin_unlock(&of_dma_lock); - return -ENODEV; + mutex_unlock(&of_dma_lock); } EXPORT_SYMBOL_GPL(of_dma_controller_free); @@ -219,15 +183,15 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np, if (of_dma_match_channel(np, name, i, &dma_spec)) continue; - ofdma = of_dma_get_controller(&dma_spec); + mutex_lock(&of_dma_lock); + ofdma = of_dma_find_controller(&dma_spec); - if (ofdma) { + if (ofdma) chan = ofdma->of_dma_xlate(&dma_spec, ofdma); - - of_dma_put_controller(ofdma); - } else { + else chan = NULL; - } + + mutex_unlock(&of_dma_lock); of_node_put(dma_spec.np); diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h index ce6a8ab..364dda7 100644 --- a/include/linux/of_dma.h +++ b/include/linux/of_dma.h @@ -25,7 +25,6 @@ struct of_dma { struct dma_chan *(*of_dma_xlate) (struct of_phandle_args *, struct of_dma *); void *of_dma_data; - int use_count; }; struct of_dma_filter_info { @@ -38,7 +37,7 @@ extern int of_dma_controller_register(struct device_node *np, struct dma_chan *(*of_dma_xlate) (struct of_phandle_args *, struct of_dma *), void *data); -extern int of_dma_controller_free(struct device_node *np); +extern void of_dma_controller_free(struct device_node *np); extern struct dma_chan *of_dma_request_slave_channel(struct device_node *np, const char *name); extern struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec, @@ -52,9 +51,8 @@ static inline int of_dma_controller_register(struct device_node *np, return -ENODEV; } -static inline int of_dma_controller_free(struct device_node *np) +static inline void of_dma_controller_free(struct device_node *np) { - return -ENODEV; } static inline struct dma_chan *of_dma_request_slave_channel(struct device_node *np, -- 2.7.4