On Wed, Jul 23, 2014 at 06:35:17PM -0700, Kuninori Morimoto wrote: > > Hi Laurent again > > > > > The rsnd_soc_dai_trigger() function takes a spinlock, making the context > > > > atomic, which regmap doesn't like as it locks a mutex. > > > > > > > > It might be possible to fix this by setting the fast_io field in both the > > > > regmap_config and regmap_bus structures in sound/soc/sh/rcar/gen.c. regmap > > > > will then use a spinlock instead of a mutex. However, even if I believe that > > > > change makes sense and should be done, another atomic context issue will > > > > come from the rcar-dmac driver which allocates memory in the > > > > prep_dma_cyclic function, called by rsnd_dma_start() from > > > > rsnd_soc_dai_trigger() with the spinlock help. > > > > > > > > What context is the rsnd_soc_dai_trigger() function called in by the alsa > > > > core ? If it's guaranteed to be a sleepable context, would it make sense to > > > > replace the rsnd_priv spinlock with a mutex ? > > > > > > Answering myself here, that's not an option, as the trigger function is called > > > in atomic context (replacing the spinlock with a mutex produced a clear BUG) > > > due to snd_pcm_lib_write1() taking a spinlock. > > > > > > Now we have a core issue. On one side there's rsnd_soc_dai_trigger() being > > > called in atomic context, and on the other side the function ends up calling > > > dmaengine_prep_dma_cyclic() which needs to allocate memory. To make this more > > > func the DMA engine API is undocumented and completely silent on whether the > > > prep functions are allowed to sleep. The question is, who's wrong ? > > > > > > Now, if you're tempted to say that I'm wrong by allocating memory with > > > GFP_KERNEL in the DMA engine driver, please read on first :-) I've tried > > > replacing GFP_KERNEL with GFP_ATOMIC allocations, and then ran into a problem > > > more complex to solve. > > > > > > The rcar-dmac DMA engine driver uses runtime PM. When not used, the device is > > > suspended. The driver calls pm_runtime_get_sync() to resume the device, and > > > needs to do so when a descriptor is submitted. This operation, currently > > > performed in the tx_submit handler, could be moved to the prep_dma_cyclic or > > > issue_pending handler, but the three operations are called in a row from > > > rsnd_dma_start(), itself ultimately called from snd_pcm_lib_write1() with the > > > spinlock held. This means I have no place in my DMA engine driver where I can > > > resume the device. > > > > > > One could argue that the rcar-dmac driver could use a work queue to handle > > > power management. That's correct, but the additional complexity, which would > > > be required in *all* DMA engine drivers, seem too high to me. If we need to go > > > that way, this is really a task that the DMA engine core should handle. > > > > > > Let's start by answering the background question and updating the DMA engine > > > API documentation once and for good : in which context are drivers allowed to > > > call the prep, tx_submit and issue_pending functions ? > > > > rsnd driver (and sound/soc/sh/fsi driver too) is using prep_dma_cyclic() now, > > but, it had been used prep_slave_single() before. > > Then, it used work queue in dai_trigger function. > > How about to use same method in prep_dma_cyclic() ? > > Do you think your issue will be solved if sound driver calls prep_dma_cyclic() > > from work queue ? > > Sorry, this doesn't solve issue. > dmaengine_prep_dma_cyclic() is used in > ${LINUX}/sound/core/pcm_dmaengine.c, > and the situation is same as ours. > > Hmm.. > In my quick check, other DMAEngine drivers are using GFP_ATOMIC > in cyclic/prep_slave_sg functions... And thats partially right. You need to use GFP_NOWAIT. -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html