diff options
author | Geert Uytterhoeven <geert+renesas@glider.be> | 2016-01-05 19:36:37 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-05-04 14:51:25 -0700 |
commit | 085dc0f08eb61f6cab5224f1f09d8a2d3ff6095a (patch) | |
tree | e7f20c0e836cb8fd29f89d7d4dd6926c913f51a2 /drivers | |
parent | 49b0033802c7eea979afd49ba89ba515f13dd373 (diff) |
serial: sh-sci: Remove cpufreq notifier to fix crash/deadlock
commit ff1cab374ad98f4b9f408525ca9c08992b4ed784 upstream.
The BSP team noticed that there is spin/mutex lock issue on sh-sci when
CPUFREQ is used. The issue is that the notifier function may call
mutex_lock() while the spinlock is held, which can lead to a BUG().
This may happen if CPUFREQ is changed while another CPU calls
clk_get_rate().
Taking the spinlock was added to the notifier function in commit
e552de2413edad1a ("sh-sci: add platform device private data"), to
protect the list of serial ports against modification during traversal.
At that time the Common Clock Framework didn't exist yet, and
clk_get_rate() just returned clk->rate without taking a mutex.
Note that since commit d535a2305facf9b4 ("serial: sh-sci: Require a
device per port mapping."), there's no longer a list of serial ports to
traverse, and taking the spinlock became superfluous.
To fix the issue, just remove the cpufreq notifier:
1. The notifier doesn't work correctly: all it does is update stored
clock rates; it does not update the divider in the hardware.
The divider will only be updated when calling sci_set_termios().
I believe this was broken back in 2004, when the old
drivers/char/sh-sci.c driver (where the notifier did update the
divider) was replaced by drivers/serial/sh-sci.c (where the
notifier just updated port->uartclk).
Cfr. full-history-linux commits 6f8deaef2e9675d9 ("[PATCH] sh: port
sh-sci driver to the new API") and 3f73fe878dc9210a ("[PATCH]
Remove old sh-sci driver").
2. On modern SoCs, the sh-sci parent clock rate is no longer related
to the CPU clock rate anyway, so using a cpufreq notifier is
futile.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/tty/serial/sh-sci.c | 39 |
1 files changed, 0 insertions, 39 deletions
diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index be33d2b0613b..0eabbac2500d 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -38,7 +38,6 @@ #include <linux/major.h> #include <linux/module.h> #include <linux/mm.h> -#include <linux/notifier.h> #include <linux/of.h> #include <linux/platform_device.h> #include <linux/pm_runtime.h> @@ -118,8 +117,6 @@ struct sci_port { struct timer_list rx_timer; unsigned int rx_timeout; #endif - - struct notifier_block freq_transition; }; /* Function prototypes */ @@ -1029,30 +1026,6 @@ static irqreturn_t sci_mpxed_interrupt(int irq, void *ptr) return ret; } -/* - * Here we define a transition notifier so that we can update all of our - * ports' baud rate when the peripheral clock changes. - */ -static int sci_notifier(struct notifier_block *self, - unsigned long phase, void *p) -{ - struct sci_port *sci_port; - unsigned long flags; - - sci_port = container_of(self, struct sci_port, freq_transition); - - if ((phase == CPUFREQ_POSTCHANGE) || - (phase == CPUFREQ_RESUMECHANGE)) { - struct uart_port *port = &sci_port->port; - - spin_lock_irqsave(&port->lock, flags); - port->uartclk = clk_get_rate(sci_port->iclk); - spin_unlock_irqrestore(&port->lock, flags); - } - - return NOTIFY_OK; -} - static struct sci_irq_desc { const char *desc; irq_handler_t handler; @@ -2406,9 +2379,6 @@ static int sci_remove(struct platform_device *dev) { struct sci_port *port = platform_get_drvdata(dev); - cpufreq_unregister_notifier(&port->freq_transition, - CPUFREQ_TRANSITION_NOTIFIER); - uart_remove_one_port(&sci_uart_driver, &port->port); sci_cleanup_single(port); @@ -2559,15 +2529,6 @@ static int sci_probe(struct platform_device *dev) if (ret) return ret; - sp->freq_transition.notifier_call = sci_notifier; - - ret = cpufreq_register_notifier(&sp->freq_transition, - CPUFREQ_TRANSITION_NOTIFIER); - if (unlikely(ret < 0)) { - sci_cleanup_single(sp); - return ret; - } - #ifdef CONFIG_SH_STANDARD_BIOS sh_bios_gdb_detach(); #endif |