[PULL,03/41] hw/timer/exynos4210_mct: Initialize ptimer before starting it

Message ID 20191022133134.14487-4-peter.maydell@linaro.org
State Accepted
Commit 1a391e20c39026f4de0d137f9b2dc64f1f8462c0
Headers show
  • target-arm queue
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Commit Message

Peter Maydell Oct. 22, 2019, 1:30 p.m.
From: Guenter Roeck <linux@roeck-us.net>

When booting a recent Linux kernel, the qemu message "Timer with delta
zero, disabling" is seen, apparently because a ptimer is started before
being initialized.  Fix the problem by initializing the offending ptimer
before starting it.

The bug is effectively harmless in the old QEMUBH setup
because the sequence of events is:
 * the delta zero means the timer expires immediately
 * ptimer_reload() arranges for exynos4210_gfrc_event() to be called
 * ptimer_reload() notices the zero delta and disables the timer
 * later, the QEMUBH runs, and exynos4210_gfrc_event() correctly
   configures the timer and restarts it

In the new transaction based API the bug is still harmless,
but differences of when the callback function runs mean the
message is not printed any more:
 * ptimer_run() does nothing as it's inside a transaction block
 * ptimer_transaction_commit() sees it has work to do and
   calls ptimer_reload()
 * the zero delta means the timer expires immediately
 * ptimer_reload() calls exynos4210_gfrc_event() directly
 * exynos4210_gfrc_event() configures the timer
 * the delta is no longer zero so ptimer_reload() doesn't complain
   (the zero-delta test is after the trigger-callback in
   the ptimer_reload() function)

Regardless, the behaviour here was not intentional, and we should
just program the ptimer correctly to start with.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Message-id: 20191018143149.9216-1-peter.maydell@linaro.org
[PMM: Expansion/clarification of the commit message:
 the message is about a zero delta, not a zero period;
 added detail to the commit message of the analysis of what
 is happening and why the kernel boots even with the message;
 added note that the message goes away with the new ptimer API]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

 hw/timer/exynos4210_mct.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)



diff --git a/hw/timer/exynos4210_mct.c b/hw/timer/exynos4210_mct.c
index 72257584145..944120aea59 100644
--- a/hw/timer/exynos4210_mct.c
+++ b/hw/timer/exynos4210_mct.c
@@ -1254,7 +1254,7 @@  static void exynos4210_mct_write(void *opaque, hwaddr offset,
         /* Start FRC if transition from disabled to enabled */
         if ((value & G_TCON_TIMER_ENABLE) > (old_val &
                 G_TCON_TIMER_ENABLE)) {
-            exynos4210_gfrc_start(&s->g_timer);
+            exynos4210_gfrc_restart(s);
         if ((value & G_TCON_TIMER_ENABLE) < (old_val &
                 G_TCON_TIMER_ENABLE)) {