lkml.org 
[lkml]   [2016]   [Mar]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/4] scatterlist: add sg_alloc_table_from_buf() helper
Hi Russell,

On Thu, 31 Mar 2016 15:14:13 +0100
Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> On Thu, Mar 31, 2016 at 02:29:42PM +0200, Boris Brezillon wrote:
> > sg_alloc_table_from_buf() provides an easy solution to create an sg_table
> > from a virtual address pointer. This function takes care of dealing with
> > vmallocated buffers, buffer alignment, or DMA engine limitations (maximum
> > DMA transfer size).
>
> Please note that the DMA API does not take account of coherency of memory
> regions other than non-high/lowmem - there are specific extensions to
> deal with this.

Ok, you said 'non-high/lowmem', this means vmalloced and kmapped buffers
already fall in this case, right?

Could you tell me more about those specific extensions?

>
> What this means is that having an API that takes any virtual address
> pointer, converts it to a scatterlist which is then DMA mapped, is
> unsafe.

Which means some implementations already get this wrong (see
spi_map_buf(), and I'm pretty sure it's not the only one).

>
> It'll be okay for PIPT and non-aliasing VIPT cache architectures, but
> for other cache architectures this will hide this problem and make
> review harder.
>

Ok, you lost me. I'll have to do my homework and try to understand what
this means :).

Thanks for your valuable inputs.

Best Regards,

Boris

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

\
 
 \ /
  Last update: 2016-03-31 17:01    [W:0.070 / U:0.548 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site