On 10/04/18 18:07, Takashi Iwai wrote:
On Tue, 10 Apr 2018 19:06:15 +0200,
Christoph Hellwig wrote:


On Tue, Apr 10, 2018 at 07:05:13PM +0200, Takashi Iwai wrote:
The code refactoring by commit 0176adb00406 ("swiotlb: refactor
coherent buffer allocation") made swiotlb_alloc_buffer() almost always
failing due to a thinko: namely, the function evaluates the
dma_coherent_ok() call incorrectly and dealing as if it's invalid.
This ends up with weird errors like iwlwifi probe failure or amdgpu
screen flickering.

This patch corrects the logic error.

This looks ok, although even hitting this code is a bad sign.  Do you
know why the previous dma_direct_alloc didn't succeed?

That I have no idea, sorry.  I just figured out the regression just
from the dmesg output of 4.16 kernel in bugzilla reports.
Could you take a look at the bugzilla reports there?

In the first one, the machine appears to have enough RAM that most of it is beyond the device's 36-bit DMA mask, thus it's fairly likely for the initial direct alloc to come back with something unsuitable.

Robin.



thanks,

Takashi

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1088658
Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1088902
Fixes: 0176adb00406 ("swiotlb: refactor coherent buffer allocation")
Cc: <sta...@vger.kernel.org> # v4.16+
Signed-off-by: Takashi Iwai <ti...@suse.de>
---
  lib/swiotlb.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 47aeb04c1997..de7cc540450f 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -719,7 +719,7 @@ swiotlb_alloc_buffer(struct device *dev, size_t size, 
dma_addr_t *dma_handle,
                goto out_warn;
*dma_handle = __phys_to_dma(dev, phys_addr);
-       if (dma_coherent_ok(dev, *dma_handle, size))
+       if (!dma_coherent_ok(dev, *dma_handle, size))
                goto out_unmap;
memset(phys_to_virt(phys_addr), 0, size);
--
2.16.3
---end quoted text---

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