On Tue, Jul 22, 2014 at 2:33 PM, Laurent Pinchart
<laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> wrote:
> @@ -740,6 +862,14 @@ rcar_dmac_chan_prep_sg(struct rcar_dmac_chan *chan, struct scatterlist *sgl,
> size = ALIGN(dev_addr, 1ULL << 32) - dev_addr;
> if (mem_addr >> 32 != (mem_addr + size - 1) >> 32)
> size = ALIGN(mem_addr, 1ULL << 32) - mem_addr;
> +
> + /*
> + * Check if either of the source or destination address
> + * can't be expressed on 32 bits. If so we can't use
s/on/in/
> + * hardware descriptors lists.
s/descriptors/descriptor/
> + */
> + if (dev_addr >> 32 || mem_addr >> 32)
> + highmem = true;
> #endif
>
> chunk = rcar_dmac_xfer_chunk_get(chan);
> @@ -770,11 +900,26 @@ rcar_dmac_chan_prep_sg(struct rcar_dmac_chan *chan, struct scatterlist *sgl,
> len -= size;
>
> list_add_tail(&chunk->node, &desc->chunks);
> + nchunks++;
> }
> }
>
> + desc->nchunks = nchunks;
> desc->size = full_size;
>
> + /*
> + * Use hardware descriptor lists if possible when more than one chunk
> + * needs to be transferred (otherwise they don't make much sense).
> + *
> + * The highmem check currently covers the whole transfer. As an
> + * optimization we could use descriptor lists for consecutive lowmem
> + * chunks and direct manual mode for highmem chunks. Whether the
> + * performance improvement would be significant enough compared to the
> + * additional complexity remains to be studied.
s/studied/investigated/
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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