• Lars-Peter Clausen's avatar
    dma:of: Use a mutex to protect the of_dma_list · de61608a
    Lars-Peter Clausen authored
    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: default avatarLars-Peter Clausen <lars@metafoo.de>
    Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
    Signed-off-by: default avatarVinod Koul <vinod.koul@intel.com>
    de61608a
of-dma.c 6.14 KB