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Subject[PATCH 2.6.34] r8169: enable 64-bit DMA by default for PCI Express devices (v2)
Currently use of 64-bit DMA is disabled in r8169 unless the user passes the
use_dac module option. This is reasonable for conventional PCI devices where
broken chipsets may not handle dual-address-cycle transfers properly for
32-bit slots and so this may not be safe. However, PCI Express should not have
this problem and not using 64-bit DMA results in DMA transfers needlessly using
the IOMMU or SWIOTLB. Set the use_dac module parameter to a new default value of
-1 which results in 64-bit DMA being enabled by default for PCI Express devices
only.

Signed-off-by: Robert Hancock <hancockrwd@gmail.com>

diff --git a/drivers/net/r8169.c b/drivers/net/r8169.c
index 616ae5a..83965ee 100644
--- a/drivers/net/r8169.c
+++ b/drivers/net/r8169.c
@@ -187,7 +187,7 @@ static DEFINE_PCI_DEVICE_TABLE(rtl8169_pci_tbl) = {
MODULE_DEVICE_TABLE(pci, rtl8169_pci_tbl);

static int rx_copybreak = 200;
-static int use_dac;
+static int use_dac = -1;
static struct {
u32 msg_enable;
} debug = { -1 };
@@ -511,7 +511,8 @@ MODULE_DESCRIPTION("RealTek RTL-8169 Gigabit Ethernet driver");
module_param(rx_copybreak, int, 0);
MODULE_PARM_DESC(rx_copybreak, "Copy breakpoint for copy-only-tiny-frames");
module_param(use_dac, int, 0);
-MODULE_PARM_DESC(use_dac, "Enable PCI DAC. Unsafe on 32 bit PCI slot.");
+MODULE_PARM_DESC(use_dac, "Enable PCI DAC. -1 defaults on for PCI Express only."
+" Unsafe on 32 bit PCI slot.");
module_param_named(debug, debug.msg_enable, int, 0);
MODULE_PARM_DESC(debug, "Debug verbosity level (0=none, ..., 16=all)");
MODULE_LICENSE("GPL");
@@ -2973,6 +2974,7 @@ rtl8169_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
void __iomem *ioaddr;
unsigned int i;
int rc;
+ int this_use_dac = use_dac;

if (netif_msg_drv(&debug)) {
printk(KERN_INFO "%s Gigabit Ethernet driver %s loaded\n",
@@ -3038,8 +3040,17 @@ rtl8169_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)

tp->cp_cmd = PCIMulRW | RxChkSum;

+ tp->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP);
+ if (!tp->pcie_cap)
+ netif_info(tp, probe, dev, "no PCI Express capability\n");
+
+ if (this_use_dac < 0)
+ this_use_dac = tp->pcie_cap != 0;
+
if ((sizeof(dma_addr_t) > 4) &&
- !pci_set_dma_mask(pdev, DMA_BIT_MASK(64)) && use_dac) {
+ this_use_dac &&
+ !pci_set_dma_mask(pdev, DMA_BIT_MASK(64))) {
+ netif_info(tp, probe, dev, "using 64-bit DMA\n");
tp->cp_cmd |= PCIDAC;
dev->features |= NETIF_F_HIGHDMA;
} else {
@@ -3058,10 +3069,6 @@ rtl8169_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
goto err_out_free_res_4;
}

- tp->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP);
- if (!tp->pcie_cap)
- netif_info(tp, probe, dev, "no PCI Express capability\n");
-
RTL_W16(IntrMask, 0x0000);

/* Soft reset the chip. */

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