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

[Geert Uytterhoeven]

Hi Rob,

On Tue, Jul 11, 2017 at 12:37 PM, Rob Landley <rob at landley.net> wrote:
> On 07/11/2017 03:59 AM, Geert Uytterhoeven wrote:
>> 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?

No, SH-SCI DMA is not used on your platform.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds