Re: Hit BUG_ON in dma-mapping.c:425 (RFC)

Artem Bityutskiy
2011-03-24T08:36:18Z

On Thu, 2011-03-24 at 08:25 +0000, Russell King - ARM Linux wrote:
> On Thu, Mar 24, 2011 at 04:18:13PM +0800, Nicolas Ferre wrote:
> > diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
> > --- a/drivers/spi/atmel_spi.c
> > +++ b/drivers/spi/atmel_spi.c
> > @@ -647,6 +647,22 @@ static void atmel_spi_next_message(struct spi_master *master)
> > atmel_spi_next_xfer(master, msg);
> > }
> >
> > +static void *adjust_buffer_location(struct device *dev, void *buf)
> > +{
> > + if (likely(buf < high_memory)) {
> > + return buf;
> > + } else {
> > + struct page *pg;
> > +
> > + pg = vmalloc_to_page(buf);
> > + if (pg == 0) {
> > + dev_err(dev, "failed to vmalloc_to_page\n");
> > + return NULL;
> > + }
> > + return page_address(pg) + ((size_t)buf & ~PAGE_MASK);
> > + }
> > +}
> > +
>
> This really doesn't fix the problem. If the page is read or written via
> the vmalloc mapping, you'll have stale data.
>
> DMA to vmalloc areas is dodgy at best.

This topics pops up often. So what is the right fix? And sorry for my
ignorance.

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)