Commit cfe275c2 authored Jun 14, 2012 by Chao Xie Committed by Greg Kroah-Hartman Jun 15, 2012

serial: pxa: add spin lock for console write



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 <chao.xie@marvell.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 2fc46915

drivers/tty/serial/pxa.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}

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