Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935374AbaBDWMz (ORCPT ); Tue, 4 Feb 2014 17:12:55 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:56733 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934026AbaBDVIu (ORCPT ); Tue, 4 Feb 2014 16:08:50 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Stephen Warren Subject: [PATCH 3.12 066/133] serial: 8250: enable UART_BUG_NOMSR for Tegra Date: Tue, 4 Feb 2014 13:07:47 -0800 Message-Id: <20140204210738.893712272@linuxfoundation.org> X-Mailer: git-send-email 1.8.5.1.163.gd7aced9 In-Reply-To: <20140204210737.008598235@linuxfoundation.org> References: <20140204210737.008598235@linuxfoundation.org> User-Agent: quilt/0.61-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stephen Warren commit 3685f19e07802ec4207b52465c408f185b66490e upstream. Tegra chips have 4 or 5 identical UART modules embedded. UARTs C..E have their MODEM-control signals tied off to a static state. However UARTs A and B can optionally route those signals to/from package pins, depending on the exact pinmux configuration. When these signals are not routed to package pins, false interrupts may trigger either temporarily, or permanently, all while not showing up in the IIR; it will read as NO_INT. This will eventually lead to the UART IRQ being disabled due to unhandled interrupts. When this happens, the kernel may print e.g.: irq 68: nobody cared (try booting with the "irqpoll" option) In order to prevent this, enable UART_BUG_NOMSR. This prevents UART_IER_MSI from being enabled, which prevents the false interrupts from triggering. In practice, this is not needed under any of the following conditions: * On Tegra chips after Tegra30, since the HW bug has apparently been fixed. * On UARTs C..E since their MODEM control signals are tied to the correct static state which doesn't trigger the issue. * On UARTs A..B if the MODEM control signals are routed out to package pins, since they will then carry valid signals. However, we ignore these exceptions for now, since they are only relevant if a board actually hooks up more than a 4-wire UART, and no currently supported board does this. If we ever support a board that does, we can refine the algorithm that enables UART_BUG_NOMSR to take those exceptions into account, and/or read a flag from DT/... that indicates that the board has hooked up and pinmux'd more than a 4-wire UART. Reported-by: Olof Johansson # autotester Signed-off-by: Stephen Warren Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_core.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -2670,6 +2670,10 @@ static void serial8250_config_port(struc if (port->type == PORT_16550A && port->iotype == UPIO_AU) up->bugs |= UART_BUG_NOMSR; + /* HW bugs may trigger IRQ while IIR == NO_INT */ + if (port->type == PORT_TEGRA) + up->bugs |= UART_BUG_NOMSR; + if (port->type != PORT_UNKNOWN && flags & UART_CONFIG_IRQ) autoconfig_irq(up); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/