Re: [Xen-devel] [PATCH 3/4] xen: set the right flags when enabling interrupts for 8250

[Chen Baozi <baozich@xxxxxxxxx>]

On Fri, Jul 19, 2013 at 10:15 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
>
> On Fri, 2013-07-19 at 20:57 +0800, Chen Baozi wrote:
> > Previous bits setting would cause generating THRE interrupts, which cannot
> > be cleared and make system loop in gic_interrupt endlessly. Set 'received
> > data available' and 'receiver line status' bits of IER when enabling
> > interrupts as what Linux 8250 driver does.
>
> We do actually want THRE interrupts though, don't we? Otherwise how do
> we know when we can send more stuff?

I'm not very sure about it. In Linux 8250 driver THRE is not set at this stage.
And following it does work for OMAP5. I'll try to dig it next to see
whether this
fix is reasonable.

>
> Are you using console_sync? It might mask any issue arising from not
> getting these interrupts (or maybe even cause your initial issue?)

Yes. I have tried to shut this down to test whether it is the cause of  my
issue. But it seems not.

>
> The LSI register is only of use if we care about RTS/CTS or something. I
> don't know if we do, but I'd be surprised if just asking for the
> interrupt was sufficient (i.e. we'd need to do something with the irq)
>
> How did you configure this interrupt line, level or edge trigger? I'd
> have expected it to need to be edge, and the issue sounds a bit like it
> might be level.

It is high-level read from the DTS. I've also changed to it to edge trigger
manually and every other possibilities when debugging. And it seems
edge trigger doesn't help.

Anyway, some research must be done for this patch and my fixes to the
issue next.

Thanks.

Baozi

>
> Ian.
>
> > Signed-off-by: Chen Baozi <baozich@xxxxxxxxx>
> > ---
> >  xen/drivers/char/ns16550.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
> > index 9248330..60512be 100644
> > --- a/xen/drivers/char/ns16550.c
> > +++ b/xen/drivers/char/ns16550.c
> > @@ -237,8 +237,8 @@ static void ns16550_setup_postirq(struct ns16550 *uart)
> >          ns_write_reg(uart,
> >                       UART_MCR, UART_MCR_OUT2 | UART_MCR_DTR | 
> > UART_MCR_RTS);
> >
> > -        /* Enable receive and transmit interrupts. */
> > -        ns_write_reg(uart, UART_IER, UART_IER_ERDAI | UART_IER_ETHREI);
> > +        /* Enable receive and line status interrupts. */
> > +        ns_write_reg(uart, UART_IER, UART_IER_ERDAI | UART_IER_ELSI);
> >      }
> >
> >      if ( uart->irq >= 0 )
>
>

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