[Cbe-oss-dev] [PATCH 5/6] spufs: fix dma restart

[Arnd Bergmann]

On Friday 15 February 2008, Luke Browning wrote:
> 
> On Fri, 2008-02-15 at 12:29 +0100, Arnd Bergmann wrote:
> 
> > 1. The mfc accesses an unmapped page
> > 2. An interrupt is signalled to the ppu
> > 3. The SPU thread breaks out of spufs_wait, while the spu keeps running
> > 4. The page fault handler makes the signal pending and restarts the DMA
> > 6a. The SPU attempts the access a second time, causing another interrupt
> > 6b. The PPU returns to user space
> > 7. The user fixes up the page mapping
> > 8. We enter spufs_run again and immediately break out of spufs_wait
> 
> 9. the exception is handled this time as the signal handler has run.
> 
> > 10. The DMA gets restarted and this time is successful.
> 
> 11. The PPU re-enters spufs_wait.
> 
> There are only two system calls made.  The exception is generated twice.
> The first time it causes a signal. The second time it is handled
> transparently within spufs_spu_run. The key is that the exception
> handling and signal handling are synchronous with respect to each other,
> since they occur in the same thread. 
> 

Right, that makes sense. Thanks for the explanation.

	Arnd <><