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staging: gasket: page table: remove extraneous memory barriers

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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: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Todd Poynor 2018-08-09 20:21:05 -07:00 committed by Greg Kroah-Hartman
parent 717264bab4
commit 7b49682bdc
1 changed files with 5 additions and 10 deletions
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15
drivers/staging/gasket/gasket_page_table.c
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@ -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;