Re: [PATCH V2] serial: exar: Preserve FCTR[5] bit in pci_xr17v35x_setup()

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

On Mon, 8 Apr 2024, Matthew Howell wrote:

> On Wed, 2024-02-21 at 16:16 -0500, Matthew Howell wrote:
> > Allows the use of the EN485 hardware pin by preserving the value of
> > FCTR[5] in pci_xr17v35x_setup().
> > 
> > Per the XR17V35X datasheet, the EN485 hardware pin works by setting
> > FCTR[5] when the pin is active. pci_xr17v35x_setup() prevented the use
> > of EN485 because it overwrote the FCTR register.
> > 
> > Signed-off-by: Matthew Howell <matthew.howell@sealevel.com>
> > ---
> > V1 -> V2
> > Fixed wordwrap in diff
> > 
> > diff --git a/drivers/tty/serial/8250/8250_exar.c b/drivers/tty/serial/8250/8250_exar.c
> > index 23366f868..97711606f 100644
> > --- a/drivers/tty/serial/8250/8250_exar.c
> > +++ b/drivers/tty/serial/8250/8250_exar.c
> > @@ -596,6 +596,7 @@ pci_xr17v35x_setup(struct exar8250 *priv, struct pci_dev *pcidev,
> >  	unsigned int baud = 7812500;
> >  	u8 __iomem *p;
> >  	int ret;
> > +	u8 en485mask;
> >  
> >  	port->port.uartclk = baud * 16;
> >  	port->port.rs485_config = platform->rs485_config;
> > @@ -618,7 +619,8 @@ pci_xr17v35x_setup(struct exar8250 *priv, struct pci_dev *pcidev,
> >  	p = port->port.membase;
> >  
> >  	writeb(0x00, p + UART_EXAR_8XMODE);
> > -	writeb(UART_FCTR_EXAR_TRGD, p + UART_EXAR_FCTR);
> > +	en485mask = readb(p + UART_EXAR_FCTR) & UART_FCTR_EXAR_485;
> > +	writeb(UART_FCTR_EXAR_TRGD | en485mask, p + UART_EXAR_FCTR);
> >  	writeb(128, p + UART_EXAR_TXTRG);
> >  	writeb(128, p + UART_EXAR_RXTRG);

Why you need to read rs485 state from the register? It should be available 
in ->rs485.flags & SER_RS485_ENABLED.

pci_fastcom335_setup() seems to have the same problem? Path small part 
seems to be common code anyway which should be moved into helper, only the 
trigger threshold seems to differ which can be given in a parameter.

-- 
 i.

> Just wanted to follow-up on this to see if anyone has had a time to
> review the above submission? Please let me know if there are any issues
> / anything I need to do.