Re: [PATCH v5 2/3] serial: 8250: Add Loongson uart driver support

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Mon, 29 Sep 2025, Jiri Slaby wrote:

> On 24. 09. 25, 8:29, Binbin Zhou wrote:
> > Add the driver for on-chip UART used on Loongson family chips.
> > 
> > The hardware is similar to 8250, but there are the following
> > differences:
> >   - Some chips (such as Loongson-2K2000) have added a fractional division
> >     register to obtain the required baud rate accurately, so the
> >     {get,set}_divisor callback is overridden.
> >   - Due to hardware defects, quirk handling is required for
> >     UART_MCR/UART_MSR.
> 
> So how hard would be to implement this in 8250 using existing (or new)
> callbacks+quirks?

??

Isn't it exactly what this submission did? It implements custom in/out 
functions which handle the xor for the relevant bits?

-- 
 i.

> > --- /dev/null
> > +++ b/drivers/tty/serial/8250/8250_loongson.c
> > @@ -0,0 +1,202 @@
> ...
> > +struct loongson_uart_data {
> > +	int line;
> > +	int mcr_invert;
> > +	int msr_invert;
> 
> These two should be unsigned. They should be u8, actually.
> 
> > +	struct reset_control *rst;
> > +};
> > +
> > +static unsigned int serial_fixup(struct uart_port *p, unsigned int offset,
> > unsigned int val)
> 
> Both 'val' and ret type should be u8.
> 
> > +{
> > +	struct loongson_uart_data *ddata = p->private_data;
> > +
> > +	if (offset == UART_MCR)
> > +		val ^= ddata->mcr_invert;
> > +
> > +	if (offset == UART_MSR)
> > +		val ^= ddata->msr_invert;
> > +
> > +	return val;
> > +}
> > +
> > +static u32 loongson_serial_in(struct uart_port *p, unsigned int offset)
> > +{
> > +	unsigned int val;
> 
> u8
> 
> > +
> > +	val = readb(p->membase + (offset << p->regshift));
> > +
> > +	return serial_fixup(p, offset, val);
> > +}
> 
> thanks,
>