[v2] serial: 8250_dw: Improve unwritable LCR workaround

Commit Message

Tim Kryger Dec. 10, 2013, 12:42 a.m. UTC

On Fri, Dec 6, 2013 at 4:59 PM, James Hogan <[e-mail]> wrote:

> It appears to work with ~0x20 too, and the workaround isn't getting hit (only
> tested boot and logging in - nothing fancy). I think having the printks in
> this code with the console directed at the serial must have caused
> resursion/busy problems somehow.

James,

I tested tested the code you proposed (cleaned up to avoid magic
numbers) on my hardware and it works fine.

                        writeb(value, p->membase + (UART_LCR << p->regshift));
@@ -132,7 +133,8 @@ static void dw8250_serial_out32(struct uart_port
*p, int offset, int value)
        if (offset == UART_LCR) {
                int tries = 1000;
                while (tries--) {
-                       if (value == p->serial_in(p, UART_LCR))
+                       unsigned int lcr = p->serial_in(p, UART_LCR);
+                       if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
                                return;
                        dw8250_force_idle(p);
                        writel(value, p->membase + (UART_LCR << p->regshift));


Would you mind posting this for proper review so we can get the fix in?

Thanks,
Tim Kryger

Comments

Ezequiel Garcia Dec. 10, 2013, 12:11 p.m. UTC | #1

Hi Tim, James:

On Mon, Dec 09, 2013 at 04:42:23PM -0800, Tim Kryger wrote:
> On Fri, Dec 6, 2013 at 4:59 PM, James Hogan <[e-mail]> wrote:
> 
[..]
> diff --git a/drivers/tty/serial/8250/8250_dw.c
> b/drivers/tty/serial/8250/8250_dw.c
> index 4658e3e..5f096c7 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -96,7 +96,8 @@ static void dw8250_serial_out(struct uart_port *p,
> int offset, int value)
>         if (offset == UART_LCR) {
>                 int tries = 1000;
>                 while (tries--) {
> -                       if (value == p->serial_in(p, UART_LCR))
> +                       unsigned int lcr = p->serial_in(p, UART_LCR);
> +                       if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
>                                 return;
>                         dw8250_force_idle(p);
>                         writeb(value, p->membase + (UART_LCR << p->regshift));
> @@ -132,7 +133,8 @@ static void dw8250_serial_out32(struct uart_port
> *p, int offset, int value)
>         if (offset == UART_LCR) {
>                 int tries = 1000;
>                 while (tries--) {
> -                       if (value == p->serial_in(p, UART_LCR))
> +                       unsigned int lcr = p->serial_in(p, UART_LCR);
> +                       if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
>                                 return;
>                         dw8250_force_idle(p);
>                         writel(value, p->membase + (UART_LCR << p->regshift));
> 
> 
> Would you mind posting this for proper review so we can get the fix in?
> 

Applying this change fixes all the problems I reported (just did a quick test on
the board I have currently on my desk).

Nice work!

James Hogan Dec. 10, 2013, 10:48 p.m. UTC | #2

On Tuesday 10 December 2013 09:11:55 Ezequiel Garcia wrote:
> Hi Tim, James:
> 
> On Mon, Dec 09, 2013 at 04:42:23PM -0800, Tim Kryger wrote:
> > On Fri, Dec 6, 2013 at 4:59 PM, James Hogan <[e-mail]> 
wrote:
> [..]
> 
> > diff --git a/drivers/tty/serial/8250/8250_dw.c
> > b/drivers/tty/serial/8250/8250_dw.c
> > index 4658e3e..5f096c7 100644
> > --- a/drivers/tty/serial/8250/8250_dw.c
> > +++ b/drivers/tty/serial/8250/8250_dw.c
> > @@ -96,7 +96,8 @@ static void dw8250_serial_out(struct uart_port *p,
> > int offset, int value)
> > 
> >         if (offset == UART_LCR) {
> >         
> >                 int tries = 1000;
> >                 while (tries--) {
> > 
> > -                       if (value == p->serial_in(p, UART_LCR))
> > +                       unsigned int lcr = p->serial_in(p, UART_LCR);
> > +                       if ((value & ~UART_LCR_SPAR) == (lcr &
> > ~UART_LCR_SPAR))> 
> >                                 return;
> >                         
> >                         dw8250_force_idle(p);
> >                         writeb(value, p->membase + (UART_LCR <<
> >                         p->regshift));
> > 
> > @@ -132,7 +133,8 @@ static void dw8250_serial_out32(struct uart_port
> > *p, int offset, int value)
> > 
> >         if (offset == UART_LCR) {
> >         
> >                 int tries = 1000;
> >                 while (tries--) {
> > 
> > -                       if (value == p->serial_in(p, UART_LCR))
> > +                       unsigned int lcr = p->serial_in(p, UART_LCR);
> > +                       if ((value & ~UART_LCR_SPAR) == (lcr &
> > ~UART_LCR_SPAR))> 
> >                                 return;
> >                         
> >                         dw8250_force_idle(p);
> >                         writel(value, p->membase + (UART_LCR <<
> >                         p->regshift));
> > 
> > Would you mind posting this for proper review so we can get the fix in?
> 
> Applying this change fixes all the problems I reported (just did a quick
> test on the board I have currently on my desk).
> 
> Nice work!

Thanks for testing it.

I've posted Tim's version for proper review with both your tested-by.

Cheers
James

Patch

diff --git a/drivers/tty/serial/8250/8250_dw.c
b/drivers/tty/serial/8250/8250_dw.c
index 4658e3e..5f096c7 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -96,7 +96,8 @@  static void dw8250_serial_out(struct uart_port *p,
int offset, int value)
        if (offset == UART_LCR) {
                int tries = 1000;
                while (tries--) {
-                       if (value == p->serial_in(p, UART_LCR))
+                       unsigned int lcr = p->serial_in(p, UART_LCR);
+                       if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
                                return;
                        dw8250_force_idle(p);