redonkable/remarkable-linux
redonkable/remarkable-linux
1
0
Fork 0
Code Releases Activity

serial: pxa: add spin lock for console write

Browse source 
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>
This commit is contained in:
Chao Xie 2012-06-14 12:18:46 +08:00 committed by Greg Kroah-Hartman
parent 2fc46915ec
commit cfe275c2db
1 changed files with 14 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
drivers/tty/serial/pxa.c
View file

@ -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);
}