On Mon, Jan 20, 2014 at 06:17:56PM +0530, Shevchenko, Andriy wrote: > On Mon, 2014-01-20 at 14:55 +0530, Vinod Koul wrote: > > On Thu, Dec 19, 2013 at 12:51:29PM +0200, Andy Shevchenko wrote: > > > On Wed, 2013-12-18 at 21:19 +0530, Vinod Koul wrote: > > > > On Mon, Dec 16, 2013 at 01:51:47PM +0530, Chew, Chiau Ee wrote: > > > > > > > > As mentioned by Andy, we are using *_noirq verion of suspend/resume > > > > > PM > > > > > callback whereby the callbacks would be executed after IRQ handlers > > > > > have been > > > > > disabled. If using SET_SYSTEM_SLEEP_PM_OPS, it would be the normal > > > > > suspend/resume PM callback. Looking at the Desginware DMAC platform > > > > > code > > > > > (drivers/dma/dw/platform.c), it is using the *_noirq suspend/resume PM > > > > > callback. Is it advisable to use the normal suspend/resume PM > > > > > callback instead > > > > > of *_noirq suspend/PM callback? > > > > > > > > i dont see a reason why we need the noirq versions > > > > > > Okay. I imagine the following use case. > > > > > > For example we have compiled in DMA driver (dw_dmac) along with, for > > > example, SPI driver. > > > > > > System was scheduled to go sleep. > > > > > > An order of calling IIUC might be DMA first, then SPI (since they are > > > not in parent / child relations). > > > > > > What was happened when SPI would like to do a DMA transfer and DMA is > > > going to sleep? I'm trying to understand if this is a case. > > In that case how does no irq version help us? > > It guarantees that we have no user of DMA anymore, since there is no > interrupt going on. well how is that. It will gaurantee that there wont be interrupt. User can still submit a transaction or another transaction will be in progress...
> > For these cases, I have been using suspend_late. Since the dmaengine driver > > is > > providing service to other clients (SPI), it needs to esnure that it > > suspends > > after SPI using suspend_late and resume using resume_early. That way dma is > > availble whenever the client is active > > suspend_late is working in context that interrupt handler may be > invoked. Thus, to have DMA driver be properly shut down we have to > wait / terminate possible ongoing transfer. Well client is already suspended via .suspend. So where is the transaction :) > > It seems for me all DMA drivers that are using > system .suspend()/.resume() are potentially buggy. Yup! -- ~Vinod -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
