On Wed, Aug 19, 2020 at 01:08:29PM +0200, Lars-Peter Clausen wrote: > > For the first option, which is potentially more performant, we have to leave the atomic PCM context > > and we are not sure if we are allowed to. > > For the second option, we would have to divide the dma_device terminate_all into an atomic sync and > > an async one, which would align with the dmaengine API, giving it the option to ensure termination > > in an atomic context. > > Based on my understanding, most of them are synchronous anyways, for the currently async ones we > > would have to implement busy waits. > > However, with this approach, we reach the WARN_ON [6] inside of an atomic context, > > indicating we might not do the right thing. > > I don't know how feasible this is to implement in the SDMA dmaengine driver. > But I think what is should do is to have some flag to indicate if a > terminate is in progress. If a new transfer is issued while terminate is in > progress the transfer should go on a list. Once terminate finishes it should > check the list and start the transfer if there are any on the list. The list is already there in form of the vchan helpers the driver uses. I think the big mistake the driver makes is to configure fields in struct sdma_channel and also the hardware directly in sdma_prep_memcpy(), sdma_prep_slave_sg() and sdma_prep_dma_cyclic(). All information should be stored in the struct sdma_desc allocated in the prep functions and only be used when it's time to fire that specific descriptor. More specifically sdma_config_write() may not be called from sdma_prep_slave_sg() or sdma_prep_dma_cyclic(), but instead must be called from sdma_start_desc(). sdma_config_ownership() also must be called later in sdma_start_desc(). 'direction' must be a member of struct sdma_desc, not of struct sdma_channel. Overall this sounds like a fair amount of work to do, but should be feasible and IMO is a step in the right direction. Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
