Reading destination and source is pointless. In DEV_TO_MEM transfers
we are only interested in the destination, in MEM_TO_DEV we care about
the source. In MEM_TO_MEM it really does not matter which one you
read.
Remove the extra pointer and select dest/source via a bool.
Reading the src/dst data from an active parameter set in the EDMA
parameter RAM is not reliable, as there might be a concurrent update
from the controller.
But experimentation showed, that a double readout with comparing the
results and a limited loop works nicely. I've actually never found a
case where the loop limit triggered, but we have it there for sanity
reasons. In case it triggers we return -EBUSY and let the caller deal
with it.
Remove the export of this function while at it. The only potential
user is the dmaengine and that's always builtin.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/arm/common/edma.c | 48 ++++++++++++++++++++++++++-----------
include/linux/platform_data/edma.h | 2 -
2 files changed, 35 insertions(+), 15 deletions(-)
Index: linux/arch/arm/common/edma.c
===================================================================
--- linux.orig/arch/arm/common/edma.c
+++ linux/arch/arm/common/edma.c
@@ -994,29 +994,49 @@ void edma_set_dest(unsigned slot, dma_ad
EXPORT_SYMBOL(edma_set_dest);
/**
- * edma_get_position - returns the current transfer points
+ * edma_get_position - returns the current transfer point
* @slot: parameter RAM slot being examined
- * @src: pointer to source port position
- * @dst: pointer to destination port position
+ * @pos: where to store the data
+ * @dst: true selects the dest position, false the source
*
- * Returns current source and destination addresses for a particular
- * parameter RAM slot. Its channel should not be active when this is called.
+ * Return 0 indicates a stable readout. -EBUSY indicates that the
+ * readout failed due to concurrent updates.
+ *
+ * Call this on active channels with care. For inactive channels this
+ * never fails.
*/
-void edma_get_position(unsigned slot, dma_addr_t *src, dma_addr_t *dst)
+int edma_get_position(unsigned slot, dma_addr_t *pos, bool dst)
{
- struct edmacc_param temp;
- unsigned ctlr;
+ u32 dat, ctlr, offs;
+ int i;
ctlr = EDMA_CTLR(slot);
slot = EDMA_CHAN_SLOT(slot);
- edma_read_slot(EDMA_CTLR_CHAN(ctlr, slot), &temp);
- if (src != NULL)
- *src = temp.src;
- if (dst != NULL)
- *dst = temp.dst;
+ if (slot >= edma_cc[ctlr]->num_slots)
+ return -EINVAL;
+
+ offs = PARM_OFFSET(slot);
+ offs += dst ? PARM_DST : PARM_SRC;
+
+ /*
+ * If the channel is active, we need to double read as we
+ * might see half updated data. We limit this to 5
+ * attempts. If that fails we return -EBUSY and let the caller
+ * deal with it.
+ */
+ dat = edma_read(ctlr, offs);
+ for (i = 0; i < 5; i++) {
+ u32 tmp = edma_read(ctlr, offs);
+
+ if (tmp == dat) {
+ *pos = dat;
+ return 0;
+ }
+ dat = tmp;
+ }
+ return -EBUSY;
}
-EXPORT_SYMBOL(edma_get_position);
/**
* edma_set_src_index - configure DMA source address indexing
Index: linux/include/linux/platform_data/edma.h
===================================================================
--- linux.orig/include/linux/platform_data/edma.h
+++ linux/include/linux/platform_data/edma.h
@@ -130,7 +130,7 @@ void edma_set_src(unsigned slot, dma_add
enum address_mode mode, enum fifo_width);
void edma_set_dest(unsigned slot, dma_addr_t dest_port,
enum address_mode mode, enum fifo_width);
-void edma_get_position(unsigned slot, dma_addr_t *src, dma_addr_t *dst);
+int __must_check edma_get_position(unsigned slot, dma_addr_t *pos, bool dst);
void edma_set_src_index(unsigned slot, s16 src_bidx, s16 src_cidx);
void edma_set_dest_index(unsigned slot, s16 dest_bidx, s16 dest_cidx);
void edma_set_transfer_params(unsigned slot, u16 acnt, u16 bcnt, u16 ccnt,
--
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