swiotlb-xen: remove start_dma_addr

It is not strictly needed. Call virt_to_phys on xen_io_tlb_start
instead. It will be useful not to have a start_dma_addr around with the
next patches.

Note that virt_to_phys is not the same as xen_virt_to_bus but actually
it is used to compared again __pa(xen_io_tlb_start) as passed to
swiotlb_init_with_tbl, so virt_to_phys is actually what we want.
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Tested-by: Corey Minyard <cminyard@mvista.com>
Tested-by: Roman Shaposhnik <roman@zededa.com>
Link: https://lore.kernel.org/r/20200710223427.6897-2-sstabellini@kernel.orgSigned-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/swiotlb-xen.c

@@ -52,8 +52,6 @@ static unsigned long xen_io_tlb_nslabs;
  * Quick lookup value of the bus address of the IOTLB.
  */
 
-static u64 start_dma_addr;
-
 /*
  * Both of these functions should avoid XEN_PFN_PHYS because phys_addr_t
  * can be 32bit when dma_addr_t is 64bit leading to a loss in
@@ -241,7 +239,6 @@ int __ref xen_swiotlb_init(int verbose, bool early)
 		m_ret = XEN_SWIOTLB_EFIXUP;
 		goto error;
 	}
-	start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
 	if (early) {
 		if (swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs,
 			 verbose))
@@ -392,8 +389,8 @@ static dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
 	 */
 	trace_swiotlb_bounced(dev, dev_addr, size, swiotlb_force);
 
-	map = swiotlb_tbl_map_single(dev, start_dma_addr, phys,
-				     size, size, dir, attrs);
+	map = swiotlb_tbl_map_single(dev, virt_to_phys(xen_io_tlb_start),
+				     phys, size, size, dir, attrs);
 	if (map == (phys_addr_t)DMA_MAPPING_ERROR)
 		return DMA_MAPPING_ERROR;