FROMLIST: staging: vsoc: Create wc kernel mapping for region shm.

Map the region shm as write-combining instead of uncachable.

Signed-off-by: Alistair Strachan <astrachan@google.com>
[sent upstream via staging https://patchwork.kernel.org/patch/10376965/]
Bug: 702147120
Change-Id: If587b4f26abaa3580b889b04dbb655f8d5b4a8ee

drivers/staging/android/TODO

@@ -31,7 +31,6 @@ vsoc.c, uapi/vsoc_shm.h
    waiting threads. We should eventually use multiple queues and select the
    queue based on the region.
  - Add debugfs support for examining the permissions of regions.
- - Use ioremap_wc instead of ioremap_nocache.
  - Remove VSOC_WAIT_FOR_INCOMING_INTERRUPT ioctl. This functionality has been
    superseded by the futex and is there for legacy reasons.
 

drivers/staging/android/vsoc.c

@@ -802,9 +802,7 @@ static int vsoc_probe_device(struct pci_dev *pdev,
 
 	dev_info(&pdev->dev, "shared memory @ DMA %p size=0x%zx\n",
 		 (void *)vsoc_dev.shm_phys_start, vsoc_dev.shm_size);
-	/* TODO(ghartman): ioremap_wc should work here */
-	vsoc_dev.kernel_mapped_shm = ioremap_nocache(
-			vsoc_dev.shm_phys_start, vsoc_dev.shm_size);
+	vsoc_dev.kernel_mapped_shm = pci_iomap_wc(pdev, SHARED_MEMORY_BAR, 0);
 	if (!vsoc_dev.kernel_mapped_shm) {
 		dev_err(&vsoc_dev.dev->dev, "cannot iomap region\n");
 		vsoc_remove_device(pdev);