This adds a new DMA subsystem API call for "weak" setting
of the DMA mask.
Weak means that it will fallback to smaller masks in case the
DMA subsystem rejects a big mask.
Currently such rejection may happen if the driver requests a 64bit
mask on a VIA machine, for example. dma_set_mask_weak() will fallback
to 32bit, in that case, and tell the caller about it by modifying the
passed mask.
Signed-off-by: Michael Buesch <mb@bu3sch.de>
Index: wireless-testing/drivers/base/dma-mapping.c
===================================================================
--- wireless-testing.orig/drivers/base/dma-mapping.c 2008-04-28 23:34:19.000000000 +0200
+++ wireless-testing/drivers/base/dma-mapping.c 2008-04-28 23:46:25.000000000 +0200
@@ -216,3 +216,38 @@ void dmam_release_declared_memory(struct
EXPORT_SYMBOL(dmam_release_declared_memory);
#endif
+
+/**
+ * dma_set_mask_weak - Set the DMA mask. Retry with smaller masks.
+ * @dev: Device to set the mask on.
+ * @mask: Pointer to the mask that you want to set. The function will
+ * modify the mask and set it to the actually used mask, in case
+ * it had to fall back to a smaller mask.
+ *
+ * Set the DMA mask and allow falling back to smaller masks in
+ * case of an error.
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+int dma_set_mask_weak(struct device *dev, u64 *mask)
+{
+ u64 m = *mask;
+ int err;
+
+ if (m < DMA_MIN_FALLBACK_MASK)
+ return -EINVAL;
+ while (1) {
+ err = dma_set_mask(dev, m);
+ if (!err)
+ break;
+ /* Did not like this one. Try a smaller one. */
+ m >>= 1;
+ if (m < DMA_MIN_FALLBACK_MASK)
+ return err;
+ }
+ *mask = m;
+
+ return 0;
+}
+EXPORT_SYMBOL(dma_set_mask_weak);
Index: wireless-testing/include/linux/dma-mapping.h
===================================================================
--- wireless-testing.orig/include/linux/dma-mapping.h 2008-04-28 23:34:19.000000000 +0200
+++ wireless-testing/include/linux/dma-mapping.h 2008-04-28 23:35:35.000000000 +0200
@@ -60,6 +60,11 @@ static inline int is_device_dma_capable(
extern u64 dma_get_required_mask(struct device *dev);
+extern int dma_set_mask_weak(struct device *dev, u64 *mask);
+/* Smallest mask fallback used by dma_set_mask_weak(). */
+#define DMA_MIN_FALLBACK_MASK DMA_BIT_MASK(24) /* 16 MB */
+
+
static inline unsigned int dma_get_max_seg_size(struct device *dev)
{
return dev->dma_parms ? dev->dma_parms->max_segment_size : 65536;
--
Greetings Michael.
--
