linux-kernel - Re: UART/TTY console deadlock

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Date:   Mon, 6 Jul 2020 23:43:14 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Petr Mladek <pmladek@...e.com>,
        Raul Rangel <rrangel@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "S, Shirish" <Shirish.S@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        John Ogness <john.ogness@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: UART/TTY console deadlock

On (20/07/06 13:31), Kurt Kanzenbach wrote:
> >> @@ -2275,6 +2275,7 @@ int serial8250_do_startup(struct uart_port *port)
> >>
> >>         if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
> >>                 unsigned char iir1;
> >> +
> >>                 /*
> >>                  * Test for UARTs that do not reassert THRE when the
> >>                  * transmitter is idle and the interrupt has already
> >> @@ -2284,8 +2285,6 @@ int serial8250_do_startup(struct uart_port *port)
> >>                  * allow register changes to become visible.
> >>                  */
> >>                 spin_lock_irqsave(&port->lock, flags);
> >> -               if (up->port.irqflags & IRQF_SHARED)
> >> -                       disable_irq_nosync(port->irq);
> >>
> >>                 wait_for_xmitr(up, UART_LSR_THRE);
> >>                 serial_port_out_sync(port, UART_IER, UART_IER_THRI);
> >> @@ -2297,8 +2296,6 @@ int serial8250_do_startup(struct uart_port *port)
> >>                 iir = serial_port_in(port, UART_IIR);
> >>                 serial_port_out(port, UART_IER, 0);
> >>
> >> -               if (port->irqflags & IRQF_SHARED)
> >> -                       enable_irq(port->irq);
> >>                 spin_unlock_irqrestore(&port->lock, flags);
> >>
> >>                 /*
> >
> > ...which effectively is a revert of
> >
> > 768aec0b5bcc ("serial: 8250: fix shared interrupts issues with SMP and
> > RT kernels")
> 
> Please, don't revert that commit. I've faced the same issue as described
> in the commit log. There is hardware available with shared UART
> interrupt lines.

Will this patch break that hardware?
https://lore.kernel.org/lkml/20200702051213.GB3450@jagdpanzerIV.localdomain/

	-ss