From 7b49682bdc6cf6f7d55e7c7e74415c2b101a9671 Mon Sep 17 00:00:00 2001 From: Todd Poynor Date: Thu, 9 Aug 2018 20:21:05 -0700 Subject: [PATCH] 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: Todd Poynor Signed-off-by: Greg Kroah-Hartman --- drivers/staging/gasket/gasket_page_table.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/drivers/staging/gasket/gasket_page_table.c b/drivers/staging/gasket/gasket_page_table.c index 4d2499269499..53492f4fad6a 100644 --- a/drivers/staging/gasket/gasket_page_table.c +++ b/drivers/staging/gasket/gasket_page_table.c @@ -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;