Re: [PATCH] amba-pl011: do not disable RTS during shutdown
From: Shreshtha Kumar SAHU
Date: Wed Jan 18 2012 - 04:36:40 EST
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