mirror of
https://github.com/openwrt/openwrt.git
synced 2024-12-25 08:21:14 +00:00
011f2c26f1
As usual these patches were extracted and rebased from the raspberry pi repo: https://github.com/raspberrypi/linux/tree/rpi-4.4.y Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
57 lines
2.2 KiB
Diff
57 lines
2.2 KiB
Diff
From 1b57eb7cd54e31f84df2378c3858a4ad2d3ab8a1 Mon Sep 17 00:00:00 2001
|
|
From: Matthias Reichl <hias@horus.com>
|
|
Date: Wed, 8 Jun 2016 13:09:56 +0200
|
|
Subject: [PATCH] dmaengine: bcm2835: Avoid splitting periods into very small
|
|
chunks
|
|
|
|
The current cyclic DMA period splitting implementation can generate
|
|
very small chunks at the end of each period. For example a 65536 byte
|
|
period will be split into a 65532 byte chunk and a 4 byte chunk on
|
|
the "lite" DMA channels.
|
|
|
|
This increases pressure on the RAM controller as the DMA controller
|
|
needs to fetch two control blocks from RAM in quick succession and
|
|
could potentially cause latency issues if the RAM is tied up by other
|
|
devices.
|
|
|
|
We can easily avoid these situations by distributing the remaining
|
|
length evenly between the last-but-one and the last chunk, making
|
|
sure that split chunks will be at least half the maximum length the
|
|
DMA controller can handle.
|
|
|
|
This patch checks if the last chunk would be less than half of
|
|
the maximum DMA length and if yes distributes the max len+4...max_len*1.5
|
|
bytes evenly between the last 2 chunks. This results in chunk sizes
|
|
between max_len/2 and max_len*0.75 bytes.
|
|
|
|
Signed-off-by: Matthias Reichl <hias@horus.com>
|
|
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
|
|
Tested-by: Clive Messer <clive.messer@digitaldreamtime.co.uk>
|
|
---
|
|
drivers/dma/bcm2835-dma.c | 14 ++++++++++++++
|
|
1 file changed, 14 insertions(+)
|
|
|
|
--- a/drivers/dma/bcm2835-dma.c
|
|
+++ b/drivers/dma/bcm2835-dma.c
|
|
@@ -253,6 +253,20 @@ static void bcm2835_dma_create_cb_set_le
|
|
|
|
/* have we filled in period_length yet? */
|
|
if (*total_len + control_block->length < period_len) {
|
|
+ /*
|
|
+ * If the next control block is the last in the period
|
|
+ * and it's length would be less than half of max_len
|
|
+ * change it so that both control blocks are (almost)
|
|
+ * equally long. This avoids generating very short
|
|
+ * control blocks (worst case would be 4 bytes) which
|
|
+ * might be problematic. We also have to make sure the
|
|
+ * new length is a multiple of 4 bytes.
|
|
+ */
|
|
+ if (*total_len + control_block->length + max_len / 2 >
|
|
+ period_len) {
|
|
+ control_block->length =
|
|
+ DIV_ROUND_UP(period_len - *total_len, 8) * 4;
|
|
+ }
|
|
/* update number of bytes in this period so far */
|
|
*total_len += control_block->length;
|
|
return;
|