of: dma: fix potential deadlock when requesting a slave channel
In the latest version of the OF dma handlers I added support (rather hastily) to exhaustively search for an available dma slave channel, for the use-case where we have alternative slave channels that can be used. In the current implementation a deadlock scenario can occur causing the CPU to loop forever. The scenario is as follows ... 1. There are alternative channels avaialble 2. The first channel that is found by calling of_dma_find_channel() is not available and so the call to the xlate function returns NULL. In this case we will call of_dma_find_channel() again but we will return the same channel that we found the first time and hence, again the xlate will return NULL and we will loop here forever. Fix this potential deadlock by just using a single for-loop and not a for-loop nested in a do-while loop. This change also replaces the function of_dma_find_channel() with of_dma_match_channel() which performs a simple check to see if a DMA channel matches the name specified. I have tested this implementation on an OMAP4 panda board by adding a dummy DMA specifier, that will cause the xlate function to return NULL, to the beginning of a list of DMA specifiers for a DMA client. Cc: Nicolas Ferre <nicolas.ferre@atmel.com> Cc: Benoit Cousson <b-cousson@ti.com> Cc: Stephen Warren <swarren@nvidia.com> Cc: Grant Likely <grant.likely@secretlab.ca> Cc: Russell King <linux@arm.linux.org.uk> Cc: Rob Herring <rob.herring@calxeda.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Vinod Koul <vinod.koul@intel.com> Cc: Dan Williams <djbw@fb.com> Signed-off-by: Jon Hunter <jon-hunter@ti.com> Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>
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