Hi Laurent > > 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 ? Best regards --- Kuninori Morimoto -- 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
