On Fri, Jul 20, 2018 at 08:23:44PM +0100, Ben Hutchings wrote:
> On Sun, 2018-07-01 at 18:02 +0200, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
> >
> > commit ce99319a182fe766be67f96338386f3ec73e321c upstream.
> >
> > When SPI transfers can be offloaded using DMA, the SPI core need to
> > build a scatterlist to make sure that the buffer to be transferred is
> > dma-able.
> >
> > This patch fixes the scatterlist entry size computation in the case
> > where the maximum acceptable scatterlist entry supported by the DMA
> > controller is less than PAGE_SIZE, when the buffer is vmalloced.
> >
> > For each entry, the actual size is given by the minimum between the
> > desc_len (which is the max buffer size supported by the DMA controller)
> > and the remaining buffer length until we cross a page boundary.
> >
> > Fixes: 65598c13fd66 ("spi: Fix per-page mapping of unaligned vmalloc-ed buffer")
> > Signed-off-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
> > Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/spi/spi.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > --- a/drivers/spi/spi.c
> > +++ b/drivers/spi/spi.c
> > @@ -707,8 +707,14 @@ static int spi_map_buf(struct spi_master
> > for (i = 0; i < sgs; i++) {
> >
> > if (vmalloced_buf) {
> > - min = min_t(size_t,
> > - len, desc_len - offset_in_page(buf));
> > + /*
> > + * Next scatterlist entry size is the minimum between
> > + * the desc_len and the remaining buffer length that
> > + * fits in a page.
> > + */
> > + min = min_t(size_t, desc_len,
> > + min_t(size_t, len,
> > + PAGE_SIZE - offset_in_page(buf)));
> > vm_page = vmalloc_to_page(buf);
> > if (!vm_page) {
> > sg_free_table(sgt);
>
> I think this makes sense upstream, but in 4.4 it seems to be a no-op
> since desc_len is always set to PAGE_SIZE when vmalloced_buf is true.
> This fix depends on (at least) commit df88e91bbfd1 "spi: respect the
> maximum segment size of DMA device" which went into 4.6.
Good catch. I'll leave it as-is for now though.
thanks,
greg k-h
