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path: root/drivers/dma/at_xdmac.c
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Diffstat (limited to 'drivers/dma/at_xdmac.c')
-rw-r--r--drivers/dma/at_xdmac.c42
1 files changed, 39 insertions, 3 deletions
diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index 64f5d1bdbb48..8e304b1befc5 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -176,6 +176,7 @@
#define AT_XDMAC_MAX_CHAN 0x20
#define AT_XDMAC_MAX_CSIZE 16 /* 16 data */
#define AT_XDMAC_MAX_DWIDTH 8 /* 64 bits */
+#define AT_XDMAC_RESIDUE_MAX_RETRIES 5
#define AT_XDMAC_DMA_BUSWIDTHS\
(BIT(DMA_SLAVE_BUSWIDTH_UNDEFINED) |\
@@ -1395,8 +1396,8 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
struct at_xdmac_desc *desc, *_desc;
struct list_head *descs_list;
enum dma_status ret;
- int residue;
- u32 cur_nda, mask, value;
+ int residue, retry;
+ u32 cur_nda, check_nda, cur_ubc, mask, value;
u8 dwidth = 0;
unsigned long flags;
@@ -1433,7 +1434,42 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
cpu_relax();
}
+ /*
+ * When processing the residue, we need to read two registers but we
+ * can't do it in an atomic way. AT_XDMAC_CNDA is used to find where
+ * we stand in the descriptor list and AT_XDMAC_CUBC is used
+ * to know how many data are remaining for the current descriptor.
+ * Since the dma channel is not paused to not loose data, between the
+ * AT_XDMAC_CNDA and AT_XDMAC_CUBC read, we may have change of
+ * descriptor.
+ * For that reason, after reading AT_XDMAC_CUBC, we check if we are
+ * still using the same descriptor by reading a second time
+ * AT_XDMAC_CNDA. If AT_XDMAC_CNDA has changed, it means we have to
+ * read again AT_XDMAC_CUBC.
+ * Memory barriers are used to ensure the read order of the registers.
+ * A max number of retries is set because unlikely it can never ends if
+ * we are transferring a lot of data with small buffers.
+ */
cur_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
+ rmb();
+ cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC);
+ for (retry = 0; retry < AT_XDMAC_RESIDUE_MAX_RETRIES; retry++) {
+ rmb();
+ check_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc;
+
+ if (likely(cur_nda == check_nda))
+ break;
+
+ cur_nda = check_nda;
+ rmb();
+ cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC);
+ }
+
+ if (unlikely(retry >= AT_XDMAC_RESIDUE_MAX_RETRIES)) {
+ ret = DMA_ERROR;
+ goto spin_unlock;
+ }
+
/*
* Remove size of all microblocks already transferred and the current
* one. Then add the remaining size to transfer of the current
@@ -1446,7 +1482,7 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
if ((desc->lld.mbr_nda & 0xfffffffc) == cur_nda)
break;
}
- residue += at_xdmac_chan_read(atchan, AT_XDMAC_CUBC) << dwidth;
+ residue += cur_ubc << dwidth;
dma_set_residue(txstate, residue);