Subject: [PATCH 3/4] mmci: sync DATAEND irq with dma|pio transfer done

From: [email-masked] (Ulf Hansson)
Date: Tue, 23 Aug 2011 12:10:31 +0200

Russell King - ARM Linux wrote:
> On Tue, Jun 28, 2011 at 09:57:40AM +0200, Linus Walleij wrote:
>> From: Ulf Hansson <[email-masked]>
>>
>> The end of a dma|pio data transfer is synced with the
>> DATAEND irq. This will prevent the mmci driver from ending
>> the request before the dma|pio job is completely done.
>>
>> For dma we use DMA_PREP_INTERRUPT to register a callback
>> function which is called when dma driver is done with job.
>>
>> To also make sure we prevent hanging forever, waiting for
>> DATAEND irq or a dma|pio transfer to be done, we setup a timer
>> when either a DATAEND or dma|pio job is done. Once both
>> conditions have occured, the timer is cancelled and the data
>> transfer is completed.
>>
>> If a timeout occurs, the data transfer is terminated in a
>> controlled manner and EAGAIN is returned to the framework.
>> A timeout value of 50 ms has been found to work well for
>> our usecases.
> 
> What is the framework supposed to do with that error code?  Magic the
> driver into disabling DMA by some non-existant callback?
> 
> Please, stop introducing magic new error codes which have no meaning to
> the upper levels unless you're also going to add some handling of those
> error conditions as well.
> 

The idea was to trigger a resend from the mmc framework, but I noticed 
that the mmc_blk_issue_rw_rq has been patched quite a lot lately. I will 
revisit this again to see if it still makes sense.