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Subject[PATCH] x86/dma-mapping: override via_no_dac for new VIA PCI bridges
Date
PCI bridges integrated in new VIA chipset/SoC have no DAC issue.
Enable DAC for the platforms with these chipset/SoC can improve DMA performance about
20% when DRAM size > 4GB.

Signed-off-by: David Wang <davidwang@zhaoxin.com>
---
arch/x86/kernel/pci-dma.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index cb9c1fa..6e37b0e 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -47,6 +47,10 @@

extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];

+#ifdef CONFIG_PCI
+static int override_via_dac __read_mostly;
+#endif
+
/* Dummy device used for NULL arguments (normally ISA). */
struct device x86_dma_fallback_dev = {
.init_name = "fallback device",
@@ -279,6 +283,9 @@ static int __init pci_iommu_init(void)

static void via_no_dac(struct pci_dev *dev)
{
+ if (override_via_dac)
+ return;
+
if (forbid_dac == 0) {
dev_info(&dev->dev, "disabling DAC on VIA PCI bridge\n");
forbid_dac = 1;
@@ -286,4 +293,19 @@ static void via_no_dac(struct pci_dev *dev)
}
DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_VIA, PCI_ANY_ID,
PCI_CLASS_BRIDGE_PCI, 8, via_no_dac);
+
+static void via_can_dac(struct pci_dev *dev)
+{
+ /*
+ * New VIA bridges have no issues for DAC.
+ * Disable the "via_no_dac" fixup code for these new VIA bridges.
+ */
+ override_via_dac = 1;
+}
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_VIA, 0x345B,
+ PCI_CLASS_BRIDGE_ISA, 8, via_can_dac);
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_VIA, 0x1001,
+ PCI_CLASS_BRIDGE_ISA, 8, via_can_dac);
+DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_VIA, 0x300A,
+ PCI_CLASS_BRIDGE_ISA, 8, via_can_dac);
#endif
--
1.9.1
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