From mboxrd@z Thu Jan 1 00:00:00 1970 From: Haojian Zhuang Subject: [PATCH v3] serial: pxa: add spin lock for console write Date: Thu, 14 Jun 2012 12:18:46 +0800 Message-ID: <1339647526-24702-1-git-send-email-haojian.zhuang@gmail.com> Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:47551 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750766Ab2FNESg (ORCPT ); Thu, 14 Jun 2012 00:18:36 -0400 Received: by pbbrp8 with SMTP id rp8so3225891pbb.19 for ; Wed, 13 Jun 2012 21:18:35 -0700 (PDT) Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: gregkh@linuxfoundation.org, linux-serial@vger.kernel.org Cc: Chao Xie , Haojian Zhuang From: Chao Xie v3: Remove empty line v2: Move local_irq_save() after clk_prepare_enable() v1: At UP mode, when cpu want to print message in kernel, it will invoke peempt_disable and disable irq. So it is safe for UP mode. For SMP mode, it is not safe to protect the HW reigsters. one CPU will run a program which will invoke printf. another CPU will run a program in kernel that invoke printk. So when second CPU is trying to printk, it will do 1. save ier register 2. enable uue bit of ier register 3. push buffer to uart fifo 4 .restore ier register when first CPU want to printf, and it happens between 1 and 4, it will enable thre bit of ier, and waiting for transmit intterupt. while step 4 will make the ier lost thre bit. add spin lock here to protect the ier register for console write. Signed-off-by: Chao Xie Signed-off-by: Haojian Zhuang --- drivers/tty/serial/pxa.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/drivers/tty/serial/pxa.c b/drivers/tty/serial/pxa.c index 5847a4b..9033fc6 100644 --- a/drivers/tty/serial/pxa.c +++ b/drivers/tty/serial/pxa.c @@ -670,9 +670,19 @@ serial_pxa_console_write(struct console *co, const char *s, unsigned int count) { struct uart_pxa_port *up = serial_pxa_ports[co->index]; unsigned int ier; + unsigned long flags; + int locked = 1; clk_prepare_enable(up->clk); + local_irq_save(flags); + if (up->port.sysrq) + locked = 0; + else if (oops_in_progress) + locked = spin_trylock(&up->port.lock); + else + spin_lock(&up->port.lock); + /* * First save the IER then disable the interrupts */ @@ -688,6 +698,10 @@ serial_pxa_console_write(struct console *co, const char *s, unsigned int count) wait_for_xmitr(up); serial_out(up, UART_IER, ier); + if (locked) + spin_unlock(&up->port.lock); + local_irq_restore(flags); + clk_disable_unprepare(up->clk); } -- 1.7.5.4