MIPS: Add implementation of dma_map_ops.mmap()

The generic implementation of dma_map_ops.mmap(), dma_common_mmap(),
is not correct for non-coherent devices. It expects to be passed a
virtual address previously returned by dma_alloc_coherent(), which for
a non-coherent device will return a KSEG1 address. It then attempts to
convert that virtual address to a physical address using virt_to_page()
which will yield an incorrect address.

Also, dma_common_mmap() does not handle the DMA_ATTR_WRITE_COMBINE
attribute, and therefore dma_mmap_writecombine() will not actually set
the appropriate pgprot_t flags for write combining.

This patch adds an implementation of dma_map_ops.mmap() that correctly
handles KSEG1 addresses, and enables write combining when requested.

Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Cc: Sadegh Abbasi <Sadegh.Abbasi@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10808/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/dma-default.c

@@ -194,6 +194,40 @@ static void mips_dma_free_coherent(struct device *dev, size_t size, void *vaddr,
 		__free_pages(page, get_order(size));
 }
 
+static int mips_dma_mmap(struct device *dev, struct vm_area_struct *vma,
+	void *cpu_addr, dma_addr_t dma_addr, size_t size,
+	struct dma_attrs *attrs)
+{
+	unsigned long user_count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+	unsigned long addr = (unsigned long)cpu_addr;
+	unsigned long off = vma->vm_pgoff;
+	unsigned long pfn;
+	int ret = -ENXIO;
+
+	if (!plat_device_is_coherent(dev) && !hw_coherentio)
+		addr = CAC_ADDR(addr);
+
+	pfn = page_to_pfn(virt_to_page((void *)addr));
+
+	if (dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs))
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+	else
+		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+	if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
+		return ret;
+
+	if (off < count && user_count <= (count - off)) {
+		ret = remap_pfn_range(vma, vma->vm_start,
+				      pfn + off,
+				      user_count << PAGE_SHIFT,
+				      vma->vm_page_prot);
+	}
+
+	return ret;
+}
+
 static inline void __dma_sync_virtual(void *addr, size_t size,
 	enum dma_data_direction direction)
 {
@@ -380,6 +414,7 @@ EXPORT_SYMBOL(dma_cache_sync);
 static struct dma_map_ops mips_default_dma_map_ops = {
 	.alloc = mips_dma_alloc_coherent,
 	.free = mips_dma_free_coherent,
+	.mmap = mips_dma_mmap,
 	.map_page = mips_dma_map_page,
 	.unmap_page = mips_dma_unmap_page,
 	.map_sg = mips_dma_map_sg,