[RFC PATCH] tty: pl011: Avoid stuck-off spurious interrupts

[Dave Martin]

On Wed, Jan 31, 2018 at 01:28:43PM +0100, Linus Walleij wrote:
> On Mon, Jan 29, 2018 at 5:09 PM, Dave Martin <Dave.Martin at arm.com> wrote:
> 
> > Commit 9b96fbacda34 ("serial: PL011: clear pending interrupts")
> > clears the RX and receive timeout interrupts on pl011 startup, to
> > avoid a screaming-interrupt scenario that can occur when the
> > firmware or bootloader leaves these interrupts spuriously
> > asserted.
> 
> It looks OK to me.

You mean, the original patch?

I think there is a real potential bug here for SBSA UART, but I also
haven't been able to reproduce it on hardware.

I'm not sure whether it can happen on a real pl011, given that the
driver turns the FIFOs off and on etc.  That may get us back into a
sane state.  On the SBSA UART this does nothing: the SBSA UART
cannot be reset or disabled directly IIRC.

> I could never reproduce this issue myself, it was just reported by
> Chanho, and we came up with this fix. AFAICR it was working fine
> on ARM reference designs and my ST-Ericsson platforms before
> and after.
> 
> I do not remember what hardware Chanho was seeing this problem
> on, but let's loop in Chanho and ask.

OK, thanks
---Dave