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Subject[PATCH] RFC: kills consistent_dma_mask
From
Date
Hi,

What do you think about this patch? It kills all references to
consistent_dma_mask in 2.6.0-test3 tree.

The consistent_dma_mask (and set_... function) is presumably a hack
which is currently not used by anything (at least in the official tree).
It's unneeded (it can be easily done in a driver, should a need arrive,
without polluting the PCI subsystem) and is not supported by "DMA" API.
It isn't even implemented on most platforms - only x86_64 and ia64 have
support for it, while on the remaining archs using it according to the
docs (with non-default value) could mean Oops or something like that.

This patch doesn't actually change any current kernel behaviour.
--
Krzysztof Halasa
Network Administrator
diff -ur linux-2.6.orig/Documentation/DMA-mapping.txt linux/Documentation/DMA-mapping.txt
--- linux-2.6.orig/Documentation/DMA-mapping.txt 2003-08-09 22:12:26.000000000 +0200
+++ linux/Documentation/DMA-mapping.txt 2003-08-17 23:55:13.000000000 +0200
@@ -87,10 +87,7 @@
PCI-X specification requires PCI-X devices to support 64-bit
addressing (DAC) for all transactions. And at least one platform (SGI
SN2) requires 64-bit consistent allocations to operate correctly when
-the IO bus is in PCI-X mode. Therefore, like with pci_set_dma_mask(),
-it's good practice to call pci_set_consistent_dma_mask() to set the
-appropriate mask even if your device only supports 32-bit DMA
-(default) and especially if it's a PCI-X device.
+the IO bus is in PCI-X mode.

For correct operation, you must interrogate the PCI layer in your
device probe routine to see if the PCI controller on the machine can
@@ -103,11 +100,6 @@

int pci_set_dma_mask(struct pci_dev *pdev, u64 device_mask);

-The query for consistent allocations is performed via a a call to
-pci_set_consistent_dma_mask():
-
- int pci_set_consistent_dma_mask(struct pci_dev *pdev, u64 device_mask);
-
Here, pdev is a pointer to the PCI device struct of your device, and
device_mask is a bit mask describing which bits of a PCI address your
device supports. It returns zero if your card can perform DMA
@@ -161,30 +153,6 @@
goto ignore_this_device;
}

-If a card is capable of using 64-bit consistent allocations as well,
-the case would look like this:
-
- int using_dac, consistent_using_dac;
-
- if (!pci_set_dma_mask(pdev, 0xffffffffffffffff)) {
- using_dac = 1;
- consistent_using_dac = 1;
- pci_set_consistent_dma_mask(pdev, 0xffffffffffffffff)
- } else if (!pci_set_dma_mask(pdev, 0xffffffff)) {
- using_dac = 0;
- consistent_using_dac = 0;
- pci_set_consistent_dma_mask(pdev, 0xffffffff)
- } else {
- printk(KERN_WARNING
- "mydev: No suitable DMA available.\n");
- goto ignore_this_device;
- }
-
-pci_set_consistent_dma_mask() will always be able to set the same or a
-smaller mask as pci_set_dma_mask(). However for the rare case that a
-device driver only uses consistent allocations, one would have to
-check the return value from pci_set_consistent_dma_mask().
-
If your 64-bit device is going to be an enormous consumer of DMA
mappings, this can be problematic since the DMA mappings are a
finite resource on many platforms. Please see the "DAC Addressing
@@ -255,8 +223,7 @@

The current default is to return consistent memory in the low 32
bits of the PCI bus space. However, for future compatibility you
- should set the consistent mask even if this default is fine for your
- driver.
+ should set the mask even if this default is fine for your driver.

Good examples of what to use consistent mappings for are:

@@ -326,15 +293,6 @@
driver needs regions sized smaller than a page, you may prefer using
the pci_pool interface, described below.

-The consistent DMA mapping interfaces, for non-NULL dev, will by
-default return a DMA address which is SAC (Single Address Cycle)
-addressable. Even if the device indicates (via PCI dma mask) that it
-may address the upper 32-bits and thus perform DAC cycles, consistent
-allocation will only return > 32-bit PCI addresses for DMA if the
-consistent dma mask has been explicitly changed via
-pci_set_consistent_dma_mask(). This is true of the pci_pool interface
-as well.
-
pci_alloc_consistent returns two values: the virtual address which you
can use to access it from the CPU and dma_handle which you pass to the
card.
diff -ur linux-2.6.orig/arch/ia64/sn/io/machvec/pci_dma.c linux/arch/ia64/sn/io/machvec/pci_dma.c
--- linux-2.6.orig/arch/ia64/sn/io/machvec/pci_dma.c 2003-07-11 21:30:44.000000000 +0200
+++ linux/arch/ia64/sn/io/machvec/pci_dma.c 2003-08-18 00:00:32.000000000 +0200
@@ -190,7 +190,7 @@
* automatically allocated a 64Bits DMA Address. Error out if the
* device cannot support DAC.
*/
- if (*dma_handle > hwdev->consistent_dma_mask) {
+ if (*dma_handle > hwdev->dma_mask) {
free_pages((unsigned long) cpuaddr, get_order(size));
return NULL;
}
diff -ur linux-2.6.orig/arch/x86_64/kernel/pci-gart.c linux/arch/x86_64/kernel/pci-gart.c
--- linux-2.6.orig/arch/x86_64/kernel/pci-gart.c 2003-08-09 22:12:32.000000000 +0200
+++ linux/arch/x86_64/kernel/pci-gart.c 2003-08-18 00:01:03.000000000 +0200
@@ -142,7 +142,7 @@
gfp |= GFP_DMA;
dma_mask = 0xffffffff;
} else {
- dma_mask = hwdev->consistent_dma_mask;
+ dma_mask = hwdev->dma_mask;
}
if (dma_mask == 0)
dma_mask = 0xffffffff;
diff -ur linux-2.6.orig/drivers/atm/lanai.c linux/drivers/atm/lanai.c
--- linux-2.6.orig/drivers/atm/lanai.c 2003-08-09 22:12:32.000000000 +0200
+++ linux/drivers/atm/lanai.c 2003-08-17 23:58:19.000000000 +0200
@@ -2039,11 +2039,6 @@
"(itf %d): No suitable DMA available.\n", lanai->number);
return -EBUSY;
}
- if (pci_set_consistent_dma_mask(pci, 0xFFFFFFFF) != 0) {
- printk(KERN_WARNING DEV_LABEL
- "(itf %d): No suitable DMA available.\n", lanai->number);
- return -EBUSY;
- }
/* Get the pci revision byte */
result = pci_read_config_byte(pci, PCI_REVISION_ID,
&lanai->pci_revision);
diff -ur linux-2.6.orig/drivers/net/tg3.c linux/drivers/net/tg3.c
--- linux-2.6.orig/drivers/net/tg3.c 2003-08-09 22:12:38.000000000 +0200
+++ linux/drivers/net/tg3.c 2003-08-17 23:57:53.000000000 +0200
@@ -6779,14 +6779,9 @@
}

/* Configure DMA attributes. */
- if (!pci_set_dma_mask(pdev, 0xffffffffffffffffULL)) {
+ if (!pci_set_dma_mask(pdev, 0xffffffffffffffffULL))
pci_using_dac = 1;
- if (pci_set_consistent_dma_mask(pdev, 0xffffffffffffffffULL)) {
- printk(KERN_ERR PFX "Unable to obtain 64 bit DMA "
- "for consistent allocations\n");
- goto err_out_free_res;
- }
- } else {
+ else {
err = pci_set_dma_mask(pdev, (u64) 0xffffffff);
if (err) {
printk(KERN_ERR PFX "No usable DMA configuration, "
diff -ur linux-2.6.orig/drivers/pci/pci.c linux/drivers/pci/pci.c
--- linux-2.6.orig/drivers/pci/pci.c 2003-08-09 22:12:40.000000000 +0200
+++ linux/drivers/pci/pci.c 2003-08-17 23:59:12.000000000 +0200
@@ -701,17 +701,6 @@
return 0;
}

-int
-pci_set_consistent_dma_mask(struct pci_dev *dev, u64 mask)
-{
- if (!pci_dma_supported(dev, mask))
- return -EIO;
-
- dev->consistent_dma_mask = mask;
-
- return 0;
-}
-
static int __devinit pci_init(void)
{
struct pci_dev *dev = NULL;
@@ -763,7 +752,6 @@
EXPORT_SYMBOL(pci_clear_mwi);
EXPORT_SYMBOL(pci_set_dma_mask);
EXPORT_SYMBOL(pci_dac_set_dma_mask);
-EXPORT_SYMBOL(pci_set_consistent_dma_mask);
EXPORT_SYMBOL(pci_assign_resource);
EXPORT_SYMBOL(pci_find_parent_resource);

diff -ur linux-2.6.orig/drivers/pci/probe.c linux/drivers/pci/probe.c
--- linux-2.6.orig/drivers/pci/probe.c 2003-08-09 22:12:40.000000000 +0200
+++ linux/drivers/pci/probe.c 2003-08-17 23:59:27.000000000 +0200
@@ -519,7 +519,6 @@
/* Assume 32-bit PCI; let 64-bit PCI cards (which are far rarer)
set this higher, assuming the system even supports it. */
dev->dma_mask = 0xffffffff;
- dev->consistent_dma_mask = 0xffffffff;
if (pci_setup_device(dev) < 0) {
kfree(dev);
return NULL;
diff -ur linux-2.6.orig/include/linux/pci.h linux/include/linux/pci.h
--- linux-2.6.orig/include/linux/pci.h 2003-08-09 22:12:47.000000000 +0200
+++ linux/include/linux/pci.h 2003-08-18 00:00:04.000000000 +0200
@@ -390,11 +390,6 @@
or supports 64-bit transfers. */
struct list_head pools; /* pci_pools tied to this device */

- u64 consistent_dma_mask;/* Like dma_mask, but for
- pci_alloc_consistent mappings as
- not all hardware supports
- 64 bit addresses for consistent
- allocations such descriptors. */
u32 current_state; /* Current operating state. In ACPI-speak,
this is D0-D3, D0 being fully functional,
and D3 being off. */
@@ -621,7 +616,6 @@
void pci_clear_mwi(struct pci_dev *dev);
int pci_set_dma_mask(struct pci_dev *dev, u64 mask);
int pci_dac_set_dma_mask(struct pci_dev *dev, u64 mask);
-int pci_set_consistent_dma_mask(struct pci_dev *dev, u64 mask);
int pci_assign_resource(struct pci_dev *dev, int i);

/* Power management related routines */
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