On Mon, 17 Dec 2007 13:17:01 +0100
Haavard Skinnemoen <[email protected]> wrote:
> > 3) NEW: optional: add-atmel-serial-dma.patch, this merged the DMA
> > code (from Chip Coldwell) in your 2.6.23 patch back on top of this
> > series. Because the AT32 bug is not been fixed for a very long time, I
> > do not expect it to be fixed soon, so I think a reordering is better
> > to make preempt-RT work on AT91.
>
> I'll give it a shot, but first I have some comments on your other
> patches.
I found a bug. The RX DMA buffer isn't invalidated before it's handed
over to the hardware. With the below patch, it seems to behave a lot
better on AVR32, but it still does funny things now and then (it seems
to dump a good chunk of stale TX data before rebooting), and magic sysrq
doesn't work.
I think I've spotted other potential races in the DMA code as well, but
they look a bit more difficult to hunt down. I'll give it another try
tomorrow.
Haavard
From: Haavard Skinnemoen <[email protected]>
Subject: [PATCH] atmel_serial: Sync DMA RX buffer after copying from it
Calling dma_sync_single_for_cpu() before reading the buffer isn't
enough. We need to call dma_sync_single_for_device() after we're done
reading as well.
Signed-off-by: Haavard Skinnemoen <[email protected]>
---
drivers/serial/atmel_serial.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/drivers/serial/atmel_serial.c b/drivers/serial/atmel_serial.c
index 0610ad9..e23a3ba 100644
--- a/drivers/serial/atmel_serial.c
+++ b/drivers/serial/atmel_serial.c
@@ -391,6 +391,8 @@ static void atmel_pdc_endrx(struct uart_port *port)
tty_insert_flip_string(tty, pdc->buf + pdc->ofs, count);
tty_flip_buffer_push(tty);
+ dma_sync_single_for_device(port->dev, pdc->dma_addr,
+ pdc->dma_size, DMA_FROM_DEVICE);
port->icount.rx += count;
}
@@ -425,6 +427,8 @@ static void atmel_pdc_timeout(struct uart_port *port)
tty_insert_flip_string(tty, pdc->buf + pdc->ofs, count);
tty_flip_buffer_push(tty);
+ dma_sync_single_for_device(port->dev, pdc->dma_addr,
+ pdc->dma_size, DMA_FROM_DEVICE);
pdc->ofs = ofs;
port->icount.rx += count;
}
--
1.5.3.4
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