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Subject[PATCH V2 13/20] dmaengine/amba-pl08x: max_bytes_per_lli is TRANSFER_SIZE * src_width (not MIN(width))
Date
max_bytes_per_lli = bd.srcbus.buswidth * PL080_CONTROL_TRANSFER_SIZE_MASK;
This is confirmed by ARM support guys.

Below is summary of mail exchange with them:

[Viresh] What is the total data to be transferred in case source and destination
bus widths are different. Suppose, source bus width is 2 bytes and destination
is 4 bytes. Now in order to transfer 80 bytes, what should be value of
TransferSize field in control reg: 40? or 20?.

[David from ARM] The value that is programmed into the TransferSize field should
be the number of <SourceWidth> transfers needed to achieve the required data
transfer.

So, to transfer 80 bytes, with a Source Width of 2, the TransferSize field =
should be programmed with:

Total transfer size
------------------- = 40
<source width>
[Viresh] Will this change if source is 4 bytes and dest is 2?

[David] Yes - the calculation then becomes:

Total transfer size
------------------- =20
<source width>
Also, max_bytes_per_lli must be calculated after fixing src and dest widths not
before that. So move this code to the correct place.

This patch also removes max_bytes_per_lli from earlier print message, as till
that point max_bytes_per_lli is unknown.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
---
drivers/dma/amba-pl08x.c | 14 ++++++--------
1 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c
index e00a9b5..c29e55c 100644
--- a/drivers/dma/amba-pl08x.c
+++ b/drivers/dma/amba-pl08x.c
@@ -601,23 +601,17 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x,
bd.srcbus.buswidth = bd.srcbus.maxwidth;
bd.dstbus.buswidth = bd.dstbus.maxwidth;

- /*
- * Bytes transferred == tsize * MIN(buswidths), not max(buswidths)
- */
- max_bytes_per_lli = min(bd.srcbus.buswidth, bd.dstbus.buswidth) *
- PL080_CONTROL_TRANSFER_SIZE_MASK;
-
/* We need to count this down to zero */
bd.remainder = txd->len;

pl08x_choose_master_bus(&bd, &mbus, &sbus, cctl);

- dev_vdbg(&pl08x->adev->dev, "src=0x%08x%s/%u dst=0x%08x%s/%u len=%zu llimax=%zu\n",
+ dev_vdbg(&pl08x->adev->dev, "src=0x%08x%s/%u dst=0x%08x%s/%u len=%zu\n",
bd.srcbus.addr, cctl & PL080_CONTROL_SRC_INCR ? "+" : "",
bd.srcbus.buswidth,
bd.dstbus.addr, cctl & PL080_CONTROL_DST_INCR ? "+" : "",
bd.dstbus.buswidth,
- bd.remainder, max_bytes_per_lli);
+ bd.remainder);
dev_vdbg(&pl08x->adev->dev, "mbus=%s sbus=%s\n",
mbus == &bd.srcbus ? "src" : "dst",
sbus == &bd.srcbus ? "src" : "dst");
@@ -657,6 +651,10 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x,
sbus->buswidth = 1;
}

+ /* Bytes transferred = tsize * src width, not MIN(buswidths) */
+ max_bytes_per_lli = bd.srcbus.buswidth *
+ PL080_CONTROL_TRANSFER_SIZE_MASK;
+
/*
* Make largest possible LLIs until less than one bus
* width left
--
1.7.2.2


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