Re: [PATCH v2] mtd: onenand: omap2: Disable DMA for HIGHMEM buffers
From: Boris Brezillon
Date: Wed May 02 2018 - 05:16:56 EST
On Wed, 2 May 2018 10:06:36 +0200
Ladislav Michl <ladis@xxxxxxxxxxxxxx> wrote:
> Hi Boris,
>
> (and apologies for delay)
>
> On Fri, Apr 20, 2018 at 10:01:34PM +0200, Boris Brezillon wrote:
> > Hi Ladislav,
> >
> > On Mon, 16 Apr 2018 08:52:59 +0200
> > Ladislav Michl <ladis@xxxxxxxxxxxxxx> wrote:
> >
> > > dma_map_single doesn't get the proper DMA address for vmalloced area,
> >
> > That's not true, it returns the right DMA (physical) address, it's just
> > that:
>
> To be honest I used log message from commit dcf08227e964 which is dealing
> with the same issue.
Okay, looks like I was wrong. The problem is caused by the
virt_to_page() call done in dma_map_single_attrs() which expects a
valid virtual address (one that is present in the identity mapping). If
you pass a vmalloc address to it, the conversion is broken and that's
probably why you end up with a NULL pointer exception.
Maybe you should just say that dma_map_single() does not work for
vmalloc-ed buffers instead of saying that it does not get the right DMA
address.