Messages in this thread | | | Date | Thu, 31 Mar 2016 16:45:57 +0200 | From | Boris Brezillon <> | Subject | Re: [PATCH 2/4] scatterlist: add sg_alloc_table_from_buf() helper |
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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
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