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Subject[RFC] pci_set_dma_mask() + doc :)
please feel free to flame or apply, I'm not sure I'm really fond of the
code example..

- z

--- linux-2.4.2/include/linux/pci.h.dmasup Wed Feb 28 10:26:14 2001
+++ linux-2.4.2/include/linux/pci.h Wed Feb 28 10:30:12 2001
@@ -527,6 +527,7 @@

int pci_enable_device(struct pci_dev *dev);
void pci_set_master(struct pci_dev *dev);
+int pci_set_dma_mask(struct pci_dev *dev, dma_addr_t mask);
int pci_set_power_state(struct pci_dev *dev, int state);
int pci_assign_resource(struct pci_dev *dev, int i);

--- linux-2.4.2/include/asm-i386/pci.h.dmasup Wed Feb 28 10:19:01 2001
+++ linux-2.4.2/include/asm-i386/pci.h Wed Feb 28 10:25:40 2001
@@ -152,6 +152,14 @@
*/
extern inline int pci_dma_supported(struct pci_dev *hwdev, dma_addr_t mask)
{
+ /*
+ * we fall back to GFP_DMA when the mask isn't all 1s,
+ * so we can't guarantee allocations that must be
+ * within a tighter range than GFP_DMA..
+ */
+ if(mask < 0x00ffffff)
+ return 0;
+
return 1;
}

--- linux-2.4.2/drivers/pci/pci.c.dmasup Wed Feb 28 10:26:34 2001
+++ linux-2.4.2/drivers/pci/pci.c Thu Mar 1 19:04:35 2001
@@ -518,6 +518,18 @@
pcibios_set_master(dev);
}

+int
+pci_set_dma_mask(struct pci_dev *dev, dma_addr_t mask)
+{
+ if(! pci_dma_supported(dev, mask))
+ return -EIO;
+
+ dev->dma_mask = mask;
+
+ return 0;
+}
+
+
/*
* Translate the low bits of the PCI base
* to the resource type
@@ -1206,6 +1218,7 @@
EXPORT_SYMBOL(pci_find_slot);
EXPORT_SYMBOL(pci_find_subsys);
EXPORT_SYMBOL(pci_set_master);
+EXPORT_SYMBOL(pci_set_dma_mask);
EXPORT_SYMBOL(pci_set_power_state);
EXPORT_SYMBOL(pci_assign_resource);
EXPORT_SYMBOL(pci_register_driver);
--- linux-2.4.2/Documentation/DMA-mapping.txt.dmasup Wed Feb 28 23:03:04 2001
+++ linux-2.4.2/Documentation/DMA-mapping.txt Thu Mar 1 19:29:38 2001
@@ -71,12 +71,35 @@
if (! pci_dma_supported(pdev, 0x00ffffff))
goto ignore_this_device;

+When DMA is possible for a given mask, the PCI layer must be informed of the
+mask for later allocation operations on the device. This is achieved by
+setting the dma_mask member of the pci_dev structure, like so:
+
+#define MY_HW_DMA_MASK 0x00ffffff
+
+ if (! pci_dma_supported(pdev, MY_HW_DMA_MASK))
+ goto ignore_this_device;
+
+ pdev->dma_mask = MY_HW_DMA_MASK;
+
+A helper function is provided which performs this common code sequence:
+
+ int pci_set_dma_mask(struct pci_dev *pdev, dma_addr_t device_mask)
+
+Unlike pci_dma_supported(), this returns -EIO when the PCI layer will not be
+able to DMA with addresses restricted by that mask, and returns 0 when DMA
+transfers are possible. If the call succeeds, the dma_mask will have been
+updated so that your driver need not worry about it.
+
There is a case which we are aware of at this time, which is worth
mentioning in this documentation. If your device supports multiple
functions (for example a sound card provides playback and record
functions) and the various different functions have _different_
DMA addressing limitations, you may wish to probe each mask and
-only provide the functionality which the machine can handle.
+only provide the functionality which the machine can handle. It
+is important that the last call to pci_set_dma_mask() be for the
+most specific mask.
+
Here is pseudo-code showing how this might be done:

#define PLAYBACK_ADDRESS_BITS 0xffffffff
@@ -86,14 +109,14 @@
struct pci_dev *pdev;

...
- if (pci_dma_supported(pdev, PLAYBACK_ADDRESS_BITS)) {
+ if (pci_set_dma_mask(pdev, PLAYBACK_ADDRESS_BITS)) {
card->playback_enabled = 1;
} else {
card->playback_enabled = 0;
printk(KERN_WARN "%s: Playback disabled due to DMA limitations.\n",
card->name);
}
- if (pci_dma_supported(pdev, RECORD_ADDRESS_BITS)) {
+ if (pci_set_dma_mask(pdev, RECORD_ADDRESS_BITS)) {
card->record_enabled = 1;
} else {
card->record_enabled = 0;
-
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