Re: 2.5.69-70 ide-cd to guarantee fault-free CD/DVD burning experience?

[Jens Axboe <axboe@suse.de>]

On Thu, May 29 2003, Andy Polyakov wrote:
> > > ... I noticed that DMA is never engaged
> > > on that buffer allocated with kmalloc. The question is if it's
> > > intentional? If answer is yes, then the case is dismissed. If not, then
> > > it should be looked into...
> > 
> > Depends on the lower level driver, for ide-cd yes kmalloc'ed data will
> > not be dma'ed to. We require a valid bio setup for that, usually the bio
> > mapping will fail exactly because the length/alignment isn't correct for
> > ide-cd.
> > 
> > > ... it might be appropriate to retry
> > > bio_map_user on buffer. I'm actually stepping out of my competence
> > > domains here...
> > 
> > It's usually not worth it. If the buffer is < 4 bytes, we don't dma. Big
> > deal.
> 
> Well, I'm concerned rather about cases when user buffer ends up in non
> DMA-able memory than small or misaligned buffers. I mean those who have
> system with loads of RAM didn't do anything wrong, yet they get
> "punished." But I'm not actually insisting! Just saying that it *might*
> be worth reconsidering "ide-cd won't do dma without bio setup" clause or
> retry bio_map_user on kalloc-ed buffer. At least for transfers not
> smaller than say 2K:-)

This is bogus. Applications already dish out the right buffers and in
the right lengths. It's the logical thing to do.

You are making up a problem that doesn't exist.

-- 
Jens Axboe