linux-kernel - Re: [PATCH] serial: 8250_pnp: Support configurable reg shift property

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Date: Thu, 29 Feb 2024 23:00:45 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: GuanBing Huang <albanhuang@...look.com>
Cc: jirislaby@...nel.org, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, albanhuang@...cent.com
Subject: Re: [PATCH] serial: 8250_pnp: Support configurable reg shift property

On Thu, Feb 29, 2024 at 07:51:54PM +0800, GuanBing Huang wrote:
> From: albanhuang <albanhuang@...cent.com>
> 
> The 16550a serial port based on the ACPI table requires obtaining the
> reg-shift attribute. In the ACPI scenario, If the reg-shift property
> is not configured like in DTS, the 16550a serial driver cannot read or
> write controller registers properly during initialization.
> 
> Signed-off-by: albanhuang <albanhuang@...cent.com>
> Signed-off-by: tombinfan <tombinfan@...cent.com>
> Signed-off-by: dylanlhdu <dylanlhdu@...cent.com>

"interesting" names, can you not just use your native encoding to make
this easier?

> ---
>  drivers/tty/serial/8250/8250_pnp.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_pnp.c b/drivers/tty/serial/8250/8250_pnp.c
> index 1974bbadc975..25b4e41e9745 100644
> --- a/drivers/tty/serial/8250/8250_pnp.c
> +++ b/drivers/tty/serial/8250/8250_pnp.c
> @@ -473,6 +473,7 @@ serial_pnp_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
>  		uart.port.flags |= UPF_SHARE_IRQ;
>  	uart.port.uartclk = 1843200;
>  	device_property_read_u32(&dev->dev, "clock-frequency", &uart.port.uartclk);
> +	device_property_read_u8(&dev->dev, "reg-shift", &uart.port.regshift);

Is this property documented somewhere?  What happens if the property
isn't there?

thanks,

greg k-h