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Commit 06e9552f authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

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: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 84564d1c

Documentation/admin-guide/kernel-parameters.txt

+0 −1
Original line number Diff line number Diff line
@@ -1705,7 +1705,6 @@ 
		nopanic

		merge

		nomerge

		forcesac

		soft

		pt		[x86, IA-64]

		nobypass	[PPC/POWERNV]

Documentation/x86/x86_64/boot-options.txt

+1 −3
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/pci-dma.c

+1 −20
Original line number Diff line number Diff line
@@ -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);

drivers/net/ethernet/sfc/efx.c

+2 −3
Original line number Diff line number Diff line
@@ -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) {

drivers/net/ethernet/sfc/falcon/efx.c

+2 −3
Original line number Diff line number Diff line
@@ -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) {