On Sun, Oct 20, 2019 at 07:10:28PM -0700, Bart Van Assche wrote:
> The effect of the dma_set_max_seg_size() call in setup_dma_device() is
> as follows:
> - If device->dev.dma_parms is NULL, that call has no effect at all.
> - If device->dev.dma_parms is not NULL, since that pointer points at
> the DMA parameters of the parent device, modify the DMA limits of the
> parent device.
>
> Both actions are wrong. Instead of changing the DMA parameters of the
> parent device, use the DMA parameters of the parent device if these
> parameters are available.
>
> Compile-tested only.
>
> Cc: Michael J. Ruhl <michael.j.ruhl@xxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Adit Ranadive <aditr@xxxxxxxxxx>
> Cc: Shiraz Saleem <shiraz.saleem@xxxxxxxxx>
> Cc: Gal Pressman <galpress@xxxxxxxxxx>
> Cc: Selvin Xavier <selvin.xavier@xxxxxxxxxxxx>
> Fixes: d10bcf947a3e ("RDMA/umem: Combine contiguous PAGE_SIZE regions in SGEs")
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> drivers/infiniband/core/device.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> index 536310fb6510..b33d684a2a99 100644
> +++ b/drivers/infiniband/core/device.c
> @@ -1199,9 +1199,18 @@ static void setup_dma_device(struct ib_device *device)
> WARN_ON_ONCE(!parent);
> device->dma_device = parent;
> }
> - /* Setup default max segment size for all IB devices */
> - dma_set_max_seg_size(device->dma_device, SZ_2G);
>
> + if (!device->dev.dma_parms) {
> + if (parent) {
> + /*
> + * The caller did not provide DMA parameters. Use the
> + * DMA parameters of the parent device.
> + */
> + device->dev.dma_parms = parent->dma_parms;
> + } else {
> + WARN_ON_ONCE(true);
> + }
> + }
> }
We really do want to, by default, increase the max_seg_size above 64k
though, so this approach doesn't seem right either.
Jason
