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From:   Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Date:   Mon, 6 Jul 2020 23:43:14 +0900
To:     Kurt Kanzenbach <kurt@linutronix.de>
Cc:     Andy Shevchenko <andy.shevchenko@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Tony Lindgren <tony@atomide.com>,
        Petr Mladek <pmladek@suse.com>,
        Raul Rangel <rrangel@google.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "S, Shirish" <Shirish.S@amd.com>,
        Peter Zijlstra <peterz@infradead.org>,
        John Ogness <john.ogness@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: UART/TTY console deadlock
Message-ID: <20200706144314.GB1485@jagdpanzerIV.localdomain>
References: <20200630102141.GA11587@alley>
 <20200630105512.GA530@jagdpanzerIV.localdomain>
 <20200630122239.GD6173@alley>
 <20200630130534.GB145027@jagdpanzerIV.localdomain>
 <20200630180255.GD37466@atomide.com>
 <20200702051213.GB3450@jagdpanzerIV.localdomain>
 <20200702160514.GK37466@atomide.com>
 <20200703103241.GB182102@jagdpanzerIV.localdomain>
 <CAHp75VdvNi_LWv7QhEsm1vQikeiMpi68qmCwoVttjnp7oq0ahg@mail.gmail.com>
 <877dvg6ft6.fsf@kurt>
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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