gpu: nvgpu: Use our own vmap() for coherent DMA buffers

For some reason the GPU does not like the mappings created by the
DMA API for coherent sysmem buffers. But a plain vmap() does seem
to work. To work around this, when we are using coherent sysmem,
force the NO_KERNEL_MAPPING flag to on and then make a vmap() in
the nvgpu DMA API wrapper. The rest of the driver will be none the
wiser but will work as expected.

This problem is not understood yet but it is being tracked in bug
2040115. Once this bug is understood this WAR should either be
determined as necessary or reverted with an appropriate fix.

Bug 2040115
JIRA EVLR-2333

Change-Id: Idae7a0c92441f0309df572ac18697af49bb6ff2b
Signed-off-by: Alex Waterman <alexw@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1657568
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/drivers/gpu/nvgpu/common/linux/pci.c b/drivers/gpu/nvgpu/common/linux/pci.c
index 4ba839c4..973da9ca 100644
--- a/drivers/gpu/nvgpu/common/linux/pci.c
+++ b/drivers/gpu/nvgpu/common/linux/pci.c
@@ -566,6 +566,12 @@ static int nvgpu_pci_probe(struct pci_dev *pdev,
         platform->g = g;
         l->dev = &pdev->dev;
 
+        np = nvgpu_get_node(g);
+        if (of_dma_is_coherent(np)) {
+                __nvgpu_set_enabled(g, NVGPU_USE_COHERENT_SYSMEM, true);
+                __nvgpu_set_enabled(g, NVGPU_SUPPORT_IO_COHERENCE, true);
+        }
+
         err = pci_enable_device(pdev);
         if (err)
                 return err;
@@ -644,13 +650,6 @@ static int nvgpu_pci_probe(struct pci_dev *pdev,
 
         g->mm.has_physical_mode = false;
 
-        np = nvgpu_get_node(g);
-
-        if (of_dma_is_coherent(np)) {
-                __nvgpu_set_enabled(g, NVGPU_USE_COHERENT_SYSMEM, true);
-                __nvgpu_set_enabled(g, NVGPU_SUPPORT_IO_COHERENCE, true);
-        }
-
         return 0;
 }