From: James Bottomley <James.Bottomley@SteelEye.com>
This patch implements dma_get_required_mask() which may be used by drivers
to probe the optimal DMA descriptor type they should be implementing on the
platform.
I've also tested it this time with the sym_2 driver...making it chose the
correct descriptors for the platform. (although I don't have a 64 bit
platform with >4GB memory, so I only confirmed it selects the 32 bit
descriptors all the time...)
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/Documentation/DMA-API.txt | 14 ++++++++++++++
25-akpm/include/linux/dma-mapping.h | 23 +++++++++++++++++++++++
25-akpm/mm/bootmem.c | 5 +++++
3 files changed, 42 insertions(+)
diff -puN Documentation/DMA-API.txt~dma_get_required_mask Documentation/DMA-API.txt
--- 25/Documentation/DMA-API.txt~dma_get_required_mask 2004-06-28 17:37:35.129480896 -0700
+++ 25-akpm/Documentation/DMA-API.txt 2004-06-28 17:37:35.137479680 -0700
@@ -162,6 +162,20 @@ parameters if it is.
Returns: 1 if successful and 0 if not
+u64
+dma_get_required_mask(struct device *dev)
+
+After setting the mask with dma_set_mask(), this API returns the
+actual mask (within that already set) that the platform actually
+requires to operate efficiently. Usually this means the returned mask
+is the minimum required to cover all of memory. Examining the
+required mask gives drivers with variable descriptor sizes the
+opportunity to use smaller descriptors as necessary.
+
+Requesting the required mask does not alter the current mask. If you
+wish to take advantage of it, you should issue another dma_set_mask()
+call to lower the mask again.
+
Part Id - Streaming DMA mappings
--------------------------------
diff -puN include/linux/dma-mapping.h~dma_get_required_mask include/linux/dma-mapping.h
--- 25/include/linux/dma-mapping.h~dma_get_required_mask 2004-06-28 17:37:35.131480592 -0700
+++ 25-akpm/include/linux/dma-mapping.h 2004-06-28 17:37:35.137479680 -0700
@@ -19,6 +19,29 @@ enum dma_data_direction {
#define dma_sync_single dma_sync_single_for_cpu
#define dma_sync_sg dma_sync_sg_for_cpu
+#ifndef ARCH_HAS_DMA_GET_REQUIRED_MASK
+static inline u64 dma_get_required_mask(struct device *dev)
+{
+ extern unsigned long max_pfn; /* defined in bootmem.h but may
+ not be included */
+ u32 low_totalram = ((max_pfn - 1) << PAGE_SHIFT);
+ u32 high_totalram = ((max_pfn - 1) >> (32 - PAGE_SHIFT));
+ u64 mask;
+
+ if (!high_totalram) {
+ /* convert to mask just covering totalram */
+ low_totalram = (1 << (fls(low_totalram) - 1));
+ low_totalram += low_totalram - 1;
+ mask = low_totalram;
+ } else {
+ high_totalram = (1 << (fls(high_totalram) - 1));
+ high_totalram += high_totalram - 1;
+ mask = (((u64)high_totalram) << 32) + 0xffffffff;
+ }
+ return mask & *dev->dma_mask;
+}
+#endif
+
#endif
diff -puN mm/bootmem.c~dma_get_required_mask mm/bootmem.c
--- 25/mm/bootmem.c~dma_get_required_mask 2004-06-28 17:37:35.133480288 -0700
+++ 25-akpm/mm/bootmem.c 2004-06-28 17:37:35.138479528 -0700
@@ -16,6 +16,7 @@
#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/mmzone.h>
+#include <linux/module.h>
#include <asm/dma.h>
#include <asm/io.h>
@@ -27,6 +28,10 @@ unsigned long max_low_pfn;
unsigned long min_low_pfn;
unsigned long max_pfn;
+EXPORT_SYMBOL(max_pfn); /* This is exported so
+ * dma_get_required_mask(), which uses
+ * it, can be an inline function */
+
/* return the number of _pages_ that will be allocated for the boot bitmap */
unsigned long __init bootmem_bootmap_pages (unsigned long pages)
{
_