Re: [PATCH] amba-pl011: do not disable RTS during shutdown

[Shreshtha Kumar SAHU]

On Tue, Jan 17, 2012 at 19:40:48 +0100, Russell King wrote:
> On Tue, Jan 17, 2012 at 03:59:49PM +0530, Shreshtha Kumar SAHU wrote:
> > From: Shreshtha Kumar Sahu <shreshthakumar.sahu@xxxxxxxxxxxxxx>
> > 
> > In present driver, shutdown clears RTS in CR register. But the
> > documentation "Documentation/serial/driver" suggests not to
> > disable RTS in shutdown(). Also RTS is preserved between shutdown
> > and startup calls, i.e. it is restored in startup if it was enabled
> > during shutdown. So that if autorts is set and RTS is set using
> > pl011_set_mctrl then it should continue even after shutdown->startup
> > sequence. And hence during set_termios it will enable RTS only if RTS
> > bit is set in UARTx_CR register. For throttling/unthrottling user
> > should call pl011_set_mctrl.
> > 
> > Change-Id: I743f33fb10e7e655657cd5dae1ec585e914a65bc
> 
> Please get rid of this line.
> 
done.
> > Signed-off-by: Shreshtha Kumar Sahu <shreshthakumar.sahu@xxxxxxxxxxxxxx>
> > Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> > ---
> >  drivers/tty/serial/amba-pl011.c |   17 ++++++++++++++++-
> >  1 files changed, 16 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> > index 6958594..46a4690 100644
> > --- a/drivers/tty/serial/amba-pl011.c
> > +++ b/drivers/tty/serial/amba-pl011.c
> > @@ -160,6 +160,7 @@ struct uart_amba_port {
> >  	unsigned int		lcrh_tx;	/* vendor-specific */
> >  	unsigned int		lcrh_rx;	/* vendor-specific */
> >  	bool			autorts;
> > +	bool			rts_state;	/* state during shutdown */
> 
> Do we really need a variable to track this?
>
As register content will be reset during low power state after shutdown.
Hence we have to preserve it during shutdown.

> >  	char			type[12];
> >  	bool			interrupt_may_hang; /* vendor-specific */
> >  #ifdef CONFIG_DMA_ENGINE
> > @@ -1412,6 +1413,8 @@ static int pl011_startup(struct uart_port *port)
> >  		barrier();
> >  
> >  	cr = UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE;
> > +	if (uap->rts_state)
> > +		cr |= UART011_CR_RTS;
> >  	writew(cr, uap->port.membase + UART011_CR);
> 
> Note that this should preserve DTR as well.
>
In the attached patch, DTR is preserved and restored.

> -- 
> Russell King
>  Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
>  maintainer of:

Best Regards,
Shreshtha