misc: bcm-vk: add mmap function for exposing BAR2

Add mmap function that allows host application to open up BAR2 memory
for remote spooling out messages from the VK logger.
Co-developed-by: Desmond Yan <desmond.yan@broadcom.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Desmond Yan <desmond.yan@broadcom.com>
Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Link: https://lore.kernel.org/r/20210120175827.14820-12-scott.branden@broadcom.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/bcm-vk/bcm_vk_dev.c

@@ -1199,6 +1199,29 @@ static long bcm_vk_reset(struct bcm_vk *vk, struct vk_reset __user *arg)
 	return ret;
 }
 
+static int bcm_vk_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct bcm_vk_ctx *ctx = file->private_data;
+	struct bcm_vk *vk = container_of(ctx->miscdev, struct bcm_vk, miscdev);
+	unsigned long pg_size;
+
+	/* only BAR2 is mmap possible, which is bar num 4 due to 64bit */
+#define VK_MMAPABLE_BAR 4
+
+	pg_size = ((pci_resource_len(vk->pdev, VK_MMAPABLE_BAR) - 1)
+		    >> PAGE_SHIFT) + 1;
+	if (vma->vm_pgoff + vma_pages(vma) > pg_size)
+		return -EINVAL;
+
+	vma->vm_pgoff += (pci_resource_start(vk->pdev, VK_MMAPABLE_BAR)
+			  >> PAGE_SHIFT);
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+	return io_remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
+				  vma->vm_end - vma->vm_start,
+				  vma->vm_page_prot);
+}
+
 static long bcm_vk_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	long ret = -EINVAL;
@@ -1237,6 +1260,7 @@ static const struct file_operations bcm_vk_fops = {
 	.write = bcm_vk_write,
 	.poll = bcm_vk_poll,
 	.release = bcm_vk_release,
+	.mmap = bcm_vk_mmap,
 	.unlocked_ioctl = bcm_vk_ioctl,
 };