x86/pci-dma: remove the experimental forcesac boot option

Limiting the dma mask to avoid PCI (pre-PCIe) DAC cycles while paying
the huge overhead of an IOMMU is rather pointless, and this seriously
gets in the way of dma mapping work.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 11fc28ecdb6d9f2ea1ce28807caf59c96c93c164..6d4a666748dd53e01bbd0624eb0006c1eb399049 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1705,7 +1705,6 @@
                nopanic
                merge
                nomerge
-               forcesac
                soft
                pt              [x86, IA-64]
                nobypass        [PPC/POWERNV]

diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
index 153b3a57fba28bd2b1871a0ed005f1d8d1cff653..341588ec4e29c7cb3aa850f176687c6a6c1cfbc2 100644 (file)
--- a/Documentation/x86/x86_64/boot-options.txt
+++ b/Documentation/x86/x86_64/boot-options.txt
@@ -208,7 +208,7 @@ IOMMU (input/output memory management unit)
       Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
 
  iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
-       [,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
+       [,memaper[=<order>]][,merge][,fullflush][,nomerge]
        [,noaperture][,calgary]
 
   General iommu options:
@@ -235,8 +235,6 @@ IOMMU (input/output memory management unit)
                        (experimental).
     nomerge            Don't do scatter-gather (SG) merging.
     noaperture         Ask the IOMMU not to touch the aperture for AGP.
-    forcesac           Force single-address cycle (SAC) mode for masks <40bits
-                       (experimental).
     noagp              Don't initialize the AGP driver and use full aperture.
     allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
                        DAC is used with 32-bit PCI to push a 64-bit address in

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index c7113fd18e320b88a1146b38b6d3c181beb43493..b65b0d7072f179b57217167456873d280a9d16f2 100644 (file)
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -20,8 +20,6 @@ static int forbid_dac __read_mostly;
 const struct dma_map_ops *dma_ops = &dma_direct_ops;
 EXPORT_SYMBOL(dma_ops);
 
-static int iommu_sac_force __read_mostly;
-
 #ifdef CONFIG_IOMMU_DEBUG
 int panic_on_overflow __read_mostly = 1;
 int force_iommu __read_mostly = 1;
@@ -122,7 +120,7 @@ static __init int iommu_setup(char *p)
                if (!strncmp(p, "nomerge", 7))
                        iommu_merge = 0;
                if (!strncmp(p, "forcesac", 8))
-                       iommu_sac_force = 1;
+                       pr_warn("forcesac option ignored.\n");
                if (!strncmp(p, "allowdac", 8))
                        forbid_dac = 0;
                if (!strncmp(p, "nodac", 5))
@@ -162,23 +160,6 @@ int arch_dma_supported(struct device *dev, u64 mask)
        }
 #endif
 
-       /* Tell the device to use SAC when IOMMU force is on.  This
-          allows the driver to use cheaper accesses in some cases.
-
-          Problem with this is that if we overflow the IOMMU area and
-          return DAC as fallback address the device may not handle it
-          correctly.
-
-          As a special case some controllers have a 39bit address
-          mode that is as efficient as 32bit (aic79xx). Don't force
-          SAC for these.  Assume all masks <= 40 bits are of this
-          type. Normally this doesn't make any difference, but gives
-          more gentle handling of IOMMU overflow. */
-       if (iommu_sac_force && (mask >= DMA_BIT_MASK(40))) {
-               dev_info(dev, "Force SAC with mask %Lx\n", mask);
-               return 0;
-       }
-
        return 1;
 }
 EXPORT_SYMBOL(arch_dma_supported);

diff --git a/drivers/net/ethernet/sfc/efx.c b/drivers/net/ethernet/sfc/efx.c
index a4ebd87154946ec11c3067139afee2c4e7395e6b..661828e8fdcf9a93017d0e5d1ada12715ba00d6a 100644 (file)
--- a/drivers/net/ethernet/sfc/efx.c
+++ b/drivers/net/ethernet/sfc/efx.c
@@ -1289,9 +1289,8 @@ static int efx_init_io(struct efx_nic *efx)
 
        pci_set_master(pci_dev);
 
-       /* Set the PCI DMA mask.  Try all possibilities from our
-        * genuine mask down to 32 bits, because some architectures
-        * (e.g. x86_64 with iommu_sac_force set) will allow 40 bit
+       /* Set the PCI DMA mask.  Try all possibilities from our genuine mask
+        * down to 32 bits, because some architectures will allow 40 bit
         * masks event though they reject 46 bit masks.
         */
        while (dma_mask > 0x7fffffffUL) {

diff --git a/drivers/net/ethernet/sfc/falcon/efx.c b/drivers/net/ethernet/sfc/falcon/efx.c
index 3d6c91e96589870ca540331350ceae7563e163c5..dd5530a4f8c8936868aed7171bd9481f93730d76 100644 (file)
--- a/drivers/net/ethernet/sfc/falcon/efx.c
+++ b/drivers/net/ethernet/sfc/falcon/efx.c
@@ -1242,9 +1242,8 @@ static int ef4_init_io(struct ef4_nic *efx)
 
        pci_set_master(pci_dev);
 
-       /* Set the PCI DMA mask.  Try all possibilities from our
-        * genuine mask down to 32 bits, because some architectures
-        * (e.g. x86_64 with iommu_sac_force set) will allow 40 bit
+       /* Set the PCI DMA mask.  Try all possibilities from our genuine mask
+        * down to 32 bits, because some architectures will allow 40 bit
         * masks event though they reject 46 bit masks.
         */
        while (dma_mask > 0x7fffffffUL) {