[PATCH 9/9] ARM: multi_v7_defconfig: Enable DMA for Renesas serial ports

[Rob Landley]

On 07/11/2017 03:59 AM, Geert Uytterhoeven wrote:
> Hi Arnd,
> 
> On Tue, Jul 11, 2017 at 10:42 AM, Arnd Bergmann <arnd at arndb.de> wrote:
>> On Tue, Jul 11, 2017 at 8:59 AM, Geert Uytterhoeven
>> <geert at linux-m68k.org> wrote:
>>> On Tue, Jul 11, 2017 at 5:38 AM, Magnus Damm <magnus.damm at gmail.com> wrote:
>>>> On Mon, Jul 10, 2017 at 10:28 PM, Geert Uytterhoeven
>>>> Since enabling DMA Engine still keeps PIO support around I wonder why
>>>> we need this Kconfig at all - other drivers seem to get by without
>>>> this kind of thing?
>>>> So in my opinion it would also be nice to get rid of SERIAL_SH_SCI_DMA
>>>> completely and reducing the number of special per-driver Kconfig
>>>> entries.
>>>
>>> In general, I would agree, and remove the option at the blimp of an eye.
>>> However, this driver is shared with H8/300 and SuperH.  While both could use
>>> DMA (but it's not supported by Linux yet), I don't know if they are willing to
>>> live with the increased static and dynamic memory footprint of SH_SCI DMA
>>> support.
>>
>> One more thing: enabling the DMA support in the console driver generally
>> means you cannot use printk in the DMA driver anywhere that may be called
>> during printk(). Not sure if that is a concern here.
> 
> Not anymore, as all of these prints should have been removed/disabled already.

Last I checked qemu-system-sh4 still doesn't work with current linux
serial driver unless you do:

--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -2193,7 +2193,7 @@ static void sci_reset(struct uart_port *port)
 			setup_timer(&s->rx_fifo_timer, rx_fifo_timer_fn,
 				    (unsigned long)s);
 		} else {
-			if (port->type == PORT_SCIFA ||
+			if (1 || port->type == PORT_SCIFA ||
 			    port->type == PORT_SCIFB)
 				scif_set_rtrg(port, 1);
 			else

Does this DMA stuff make that situation worse?

Rob