Hi Geert,

On 11 July 2018 13:42, Geert Uytterhoeven wrote:
> On Wed, Jul 11, 2018 at 2:30 PM Phil Edworthy wrote:
> > The Renesas RZ/N1 UART is based on the Synopsys DW UART, but has
> > additional registers for DMA. This patch does not address the changes
> > required for DMA support, it simply adds the compatible string.
> >
> > Signed-off-by: Phil Edworthy <phil.edwor...@renesas.com>
> 
> Thanks for your patch!
> 
> What happens if someone would boot a kernel that has only this patch
> applied and a DTB that already has the to-be-supported dmas properties?
The driver only sets up dma if the fifo depth is >0, and this is read from
CPR register. This is an optional (as in RTL configuration) register for the
Synopsys UART block. On rzn1 devices, this register returns 0, so the
driver will not set up dma => so the uart still works.

Additionally, the uart normally used for the console (used because the 
BootROM uses it) does not have any dma capabilities.

Thanks
Phil

> > --- a/drivers/tty/serial/8250/8250_dw.c
> > +++ b/drivers/tty/serial/8250/8250_dw.c
> > @@ -693,6 +693,7 @@ static const struct of_device_id dw8250_of_match[]
> = {
> >         { .compatible = "snps,dw-apb-uart" },
> >         { .compatible = "cavium,octeon-3860-uart" },
> >         { .compatible = "marvell,armada-38x-uart" },
> > +       { .compatible = "renesas,uart-rzn1" },
> 
> renesas,rzn1-uart
> 
> >         { /* Sentinel */ }
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@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

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