Re: [Xen-devel] [PATCH v2 1/2] ns16550: Add compatible string for Raspberry Pi 4

[Andre Przywara <andre.przywara@xxxxxxx>]

On Mon, 29 Jul 2019 09:19:19 -0400
Stewart Hildebrand <stewart.hildebrand@xxxxxxxxxxxxxxx> wrote:

Hi,

> Per the BCM2835 peripherals datasheet [1] page 10:
> "The UART core is build to emulate 16550 behaviour ... The implemented
> UART is not a 16650 compatible UART However as far as possible the
> first 8 control and status registers are laid out like a 16550 UART. Al
> 16550 register bits which are not supported can be written but will be
> ignored and read back as 0. All control bits for simple UART receive/
> transmit operations are available."
> 
> Additionally, Linux uses the 8250/16550 driver for the aux UART [2].
> 
> Unfortunately the brcm,bcm2835-aux-uart device tree binding doesn't
> have the reg-shift and reg-io-width properties [3]. Thus, the reg-shift
> and reg-io-width properties are inherent properties of this UART.
> 
> Thanks to Andre Przywara for contributing the reg-shift and
> reg-io-width setting snippet.
> 
> In my testing, I have relied on enable_uart=1 being set in config.txt,
> a configuration file read by the Raspberry Pi's firmware. With
> enable_uart=1, the firmware performs UART initialization.
> 
> [1] 
> https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2835/BCM2835-ARM-Peripherals.pdf
> [2] 
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/tty/serial/8250/8250_bcm2835aux.c
> [3] 
> https://www.kernel.org/doc/Documentation/devicetree/bindings/serial/brcm,bcm2835-aux-uart.txt
> 
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxxxxxxxxxx>

Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
Tested-by: Andre Przywara <andre.przywara@xxxxxxx>

Cheers,
Andre.

> ---
>  xen/drivers/char/ns16550.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
> index e518f2d790..8667de6d67 100644
> --- a/xen/drivers/char/ns16550.c
> +++ b/xen/drivers/char/ns16550.c
> @@ -1585,6 +1585,12 @@ static int __init ns16550_uart_dt_init(struct 
> dt_device_node *dev,
>      if ( uart->reg_width != 1 && uart->reg_width != 4 )
>          return -EINVAL;
>  
> +    if ( dt_device_is_compatible(dev, "brcm,bcm2835-aux-uart") )
> +    {
> +        uart->reg_width = 4;
> +        uart->reg_shift = 2;
> +    }
> +
>      res = platform_get_irq(dev, 0);
>      if ( ! res )
>          return -EINVAL;
> @@ -1611,6 +1617,7 @@ static const struct dt_device_match ns16550_dt_match[] 
> __initconst =
>      DT_MATCH_COMPATIBLE("ns16550"),
>      DT_MATCH_COMPATIBLE("ns16550a"),
>      DT_MATCH_COMPATIBLE("snps,dw-apb-uart"),
> +    DT_MATCH_COMPATIBLE("brcm,bcm2835-aux-uart"),
>      { /* sentinel */ },
>  };
>  


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel