[01/12] misc: vexpress-syscfg: Add udelay-based delay

Commit Message

Pawel Moll Feb. 11, 2014, 5:10 p.m. UTC

It is normally preferable to yield the task
waiting for syscfg operations (that can take
up to dozens of milliseconds), but when the
system is shutting down it may not be possible.

This patch adds a udelay-based version of the
code to be used in such circumstances.

Cc: Arnd Bergmann <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Pawel Moll <[e-mail]>
---
 drivers/misc/vexpress-syscfg.c | 40 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

Comments

Greg Kroah-Hartman Feb. 15, 2014, 7:19 p.m. UTC | #1

On Tue, Feb 11, 2014 at 05:10:25PM +0000, Pawel Moll wrote:
> It is normally preferable to yield the task
> waiting for syscfg operations (that can take
> up to dozens of milliseconds), but when the
> system is shutting down it may not be possible.

Really?  What happens at shutdown that prevents things from being
scheduled?  Why would you want to busy-loop instead at this point in
time?

thanks,

greg k-h

Patch

diff --git a/drivers/misc/vexpress-syscfg.c b/drivers/misc/vexpress-syscfg.c
index 4d661ef..82f8229 100644
--- a/drivers/misc/vexpress-syscfg.c
+++ b/drivers/misc/vexpress-syscfg.c
@@ -53,6 +53,37 @@  struct vexpress_syscfg_func {
 };
 
 
+static int vexpress_syscfg_delay_schedule(unsigned int us)
+{
+	set_current_state(TASK_INTERRUPTIBLE);
+	schedule_timeout(usecs_to_jiffies(us));
+	if (signal_pending(current))
+		return -EINTR;
+
+	return 0;
+}
+
+static int vexpress_syscfg_delay_loop(unsigned int us)
+{
+	udelay(us);
+
+	return 0;
+}
+
+static int (*vexpress_syscfg_delay)(unsigned int us) =
+		vexpress_syscfg_delay_schedule;
+
+static void vexpress_syscfg_shutdown(void)
+{
+	/* Can't relay on the scheduler when the system is going down */
+	vexpress_syscfg_delay = vexpress_syscfg_delay_loop;
+}
+
+static struct syscore_ops vexpress_syscfg_syscore_ops = {
+	.shutdown = vexpress_syscfg_shutdown,
+};
+
+
 static int vexpress_syscfg_exec(struct vexpress_syscfg_func *func,
 		int index, bool write, u32 *data)
 {
@@ -87,10 +118,9 @@  static int vexpress_syscfg_exec(struct vexpress_syscfg_func *func,
 	tries = 100;
 	timeout = 100;
 	do {
-		set_current_state(TASK_INTERRUPTIBLE);
-		schedule_timeout(usecs_to_jiffies(timeout));
-		if (signal_pending(current))
-			return -EINTR;
+		int err = vexpress_syscfg_delay(timeout);
+		if (err)
+			return err;
 
 		status = readl(syscfg->base + SYS_CFGSTAT);
 		if (status & SYS_CFGSTAT_ERR)
@@ -299,6 +329,8 @@  int vexpress_syscfg_probe(struct platform_device *pdev)
 	if (!pdev->dev.of_node)
 		vexpress_syscfg_bridge = bridge;
 
+	register_syscore_ops(&vexpress_syscfg_syscore_ops);
+
 	return 0;
 }