On 09/11/2014 01:17 PM, Heikki Krogerus wrote:

quoted

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index fbed1636e9c4..09489b391568 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h

@@ -82,6 +82,9 @@ struct serial8250_config {
 #define UART_BUG_PARITY	(1 << 4)	/* UART mishandles parity if FIFO enabled */
 #define UART_BUG_DMA_RX	(1 << 5)	/* UART needs DMA RX req before there is
 					   data in FIFO */
+#define UART_BUG_DMA_TX	(1 << 6)	/* UART needs one byte in FIFO for
+					   kickstart */

I don't think we should go ahead with this patch. I'm pretty sure
this is AM335 specific problem, or at least limited to only few
platforms. And I don't think we should take any more "BUG" flags.

We should add hooks like tx_dma and rx_dma to struct uart_8250_dma so
that the probe drivers can replace serial8250_tx_dma and
seria8250_rx_dma, like I think Alan already suggested.

Okay. Wasn't aware that Alan already suggested that.
I also need a watchdog timer for TX since it seems that on omap3 the
DMA engine suddenly forgets to continue with DMA?

If this is really what we want, I would need to refactor a few things?

Let's keep serial8250_tx_dma/rx_dma as the default, and not add any
quirks to them. Only if there is a very common case should it be
handled in those. The case of RX req needing to be sent before data in
FIFO maybe one of those, but I'm no sure.

keep in mind that both (RX & TX bugs/hacks) need also a bit of handling
in the 8250-core so it works together (like the tx_err member so we
fall back to manual xmit)

Sebastian