On Fri, Oct 28, 2016 at 10:34 AM, Konrad Rzeszutek Wilk
[off-list ref] wrote:

On Tue, Oct 25, 2016 at 11:37:03AM -0400, Alexander Duyck wrote:

quoted

As a first step to making DMA_ATTR_SKIP_CPU_SYNC apply to architectures
beyond just ARM I need to make it so that the swiotlb will respect the
flag.  In order to do that I also need to update the swiotlb-xen since it
heavily makes use of the functionality.

Cc: Konrad Rzeszutek Wilk <redacted>

I am pretty sure I acked it the RFC. Was there a particular
reason (this is very different from the RFC?) you dropped my ACk?

Thanks.

If I recall you had acked patch 1, but for 2 you had some review
comments on and suggested I change a few things.  What was patch 2 in
the RFC was split out into patches 2 and 3.  That is why I didn't
include an Ack from you for those patches.

Patch 2 is a fix for Xen to address the fact that you could return
either 0 or ~0.  It was part of patch 2 originally and I pulled it out
into a separate patch.

Patch 3 does most of what patch 2 in the RFC was doing before with
fixes to address the fact that I was moving some code to avoid going
over 80 characters.  I found a different way to fix that by just
updating attrs before using it instead of ORing in the value when
passing it as a parameter.

quoted

@@ -558,11 +560,12 @@ void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
                                                               start_dma_addr,
                                                               sg_phys(sg),
                                                               sg->length,
-                                                              dir);
+                                                              dir, attrs);
                      if (map == SWIOTLB_MAP_ERROR) {
                              dev_warn(hwdev, "swiotlb buffer is full\n");
                              /* Don't panic here, we expect map_sg users
                                 to do proper error handling. */
+                             attrs |= DMA_ATTR_SKIP_CPU_SYNC;
                              xen_swiotlb_unmap_sg_attrs(hwdev, sgl, i, dir,
                                                         attrs);
                              sg_dma_len(sgl) = 0;

The biggest difference from patch 2 in the RFC is right here.  This
code before was moving this off to the end of the function and adding
a label which I then jumped to.  I just ORed the
DMA_ATTR_SKIP_CPU_SYNC into attrs and skipped the problem entirely.
It should be harmless to do this way since attrs isn't used anywhere
else once we have had the error.

I hope that helps to clear it up.  So if you want I will add your
Acked-by for patches 2 and 3, but I just wanted to make sure this
worked with the changes you suggested.

Thanks.

- Alex