Commit 7b49682b authored by Todd Poynor's avatar Todd Poynor Committed by Greg Kroah-Hartman
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staging: gasket: page table: remove extraneous memory barriers 



Some explicit memory barriers in the page table code are not necessary,
either because:

(a) The barrier follows a non-relaxed MMIO access that already performs
a read or write memory barrier.

(b) The barrier follows DMA API calls for which the device-visible
effects of IOMMU programming are guaranteed to be flushed to the IOMMU
prior to the call returning, and doesn't need to sync with normal memory
access.

Signed-off-by: default avatarTodd Poynor <toddpoynor@google.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 717264ba

drivers/staging/gasket/gasket_page_table.c

+5 −10
Original line number Diff line number Diff line
@@ -317,8 +317,6 @@ static void gasket_free_extended_subtable(struct gasket_page_table *pg_tbl, 


	/* Release the page table from the device */

	writeq(0, slot);

	/* Force sync around the address release. */

	mb();



	if (pte->dma_addr)

		dma_unmap_page(pg_tbl->device, pte->dma_addr, PAGE_SIZE,
@@ -504,8 +502,6 @@ static int gasket_perform_mapping(struct gasket_page_table *pg_tbl, 
					(void *)page_to_phys(page));

				return -1;

			}

			/* Wait until the page is mapped. */

			mb();

		}



		/* Make the DMA-space address available to the device. */
@@ -604,12 +600,13 @@ static void gasket_perform_unmapping(struct gasket_page_table *pg_tbl, 
	 */

	for (i = 0; i < num_pages; i++) {

		/* release the address from the device, */

		if (is_simple_mapping || ptes[i].status == PTE_INUSE)

		if (is_simple_mapping || ptes[i].status == PTE_INUSE) {

			writeq(0, &slots[i]);

		else

		} else {

			((u64 __force *)slots)[i] = 0;

		/* Force sync around the address release. */

		mb();

			/* sync above PTE update before updating mappings */

			wmb();

		}



		/* release the address from the driver, */

		if (ptes[i].status == PTE_INUSE) {
@@ -898,8 +895,6 @@ static int gasket_alloc_extended_subtable(struct gasket_page_table *pg_tbl, 
	/* Map the page into DMA space. */

	pte->dma_addr = dma_map_page(pg_tbl->device, pte->page, 0, PAGE_SIZE,

				     DMA_BIDIRECTIONAL);

	/* Wait until the page is mapped. */

	mb();



	/* make the addresses available to the device */

	dma_addr = (pte->dma_addr + pte->offset) | GASKET_VALID_SLOT_FLAG;

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