From a7a305aee1e9a74a3f4b263aa98babed795b1f0a Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 3 Jul 2017 16:13:32 +0100 Subject: [PATCH] include/hw/ptimer.h: Add documentation comments MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Add documentation comments describing the public API of the ptimer countdown timer. Signed-off-by: Peter Maydell Reviewed-by: Philippe Mathieu-Daudé Signed-off-by: Michael Tokarev --- include/hw/ptimer.h | 120 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 120 insertions(+) diff --git a/include/hw/ptimer.h b/include/hw/ptimer.h index eafc3f0a86..fc4ef5cc1d 100644 --- a/include/hw/ptimer.h +++ b/include/hw/ptimer.h @@ -12,6 +12,20 @@ #include "qemu/timer.h" #include "migration/vmstate.h" +/* The ptimer API implements a simple periodic countdown timer. + * The countdown timer has a value (which can be read and written via + * ptimer_get_count() and ptimer_set_count()). When it is enabled + * using ptimer_run(), the value will count downwards at the frequency + * which has been configured using ptimer_set_period() or ptimer_set_freq(). + * When it reaches zero it will trigger a QEMU bottom half handler, and + * can be set to either reload itself from a specified limit value + * and keep counting down, or to stop (as a one-shot timer). + * + * Forgetting to set the period/frequency (or setting it to zero) is a + * bug in the QEMU device and will cause warning messages to be printed + * to stderr when the guest attempts to enable the timer. + */ + /* The default ptimer policy retains backward compatibility with the legacy * timers. Custom policies are adjusting the default one. Consider providing * a correct policy for your timer. @@ -59,15 +73,121 @@ typedef struct ptimer_state ptimer_state; typedef void (*ptimer_cb)(void *opaque); +/** + * ptimer_init - Allocate and return a new ptimer + * @bh: QEMU bottom half which is run on timer expiry + * @policy: PTIMER_POLICY_* bits specifying behaviour + * + * The ptimer returned must be freed using ptimer_free(). + * The ptimer takes ownership of @bh and will delete it + * when the ptimer is eventually freed. + */ ptimer_state *ptimer_init(QEMUBH *bh, uint8_t policy_mask); + +/** + * ptimer_free - Free a ptimer + * @s: timer to free + * + * Free a ptimer created using ptimer_init() (including + * deleting the bottom half which it is using). + */ void ptimer_free(ptimer_state *s); + +/** + * ptimer_set_period - Set counter increment interval in nanoseconds + * @s: ptimer to configure + * @period: period of the counter in nanoseconds + * + * Note that if your counter behaviour is specified as having a + * particular frequency rather than a period then ptimer_set_freq() + * may be more appropriate. + */ void ptimer_set_period(ptimer_state *s, int64_t period); + +/** + * ptimer_set_freq - Set counter frequency in Hz + * @s: ptimer to configure + * @freq: counter frequency in Hz + * + * This does the same thing as ptimer_set_period(), so you only + * need to call one of them. If the counter behaviour is specified + * as setting the frequency then this function is more appropriate, + * because it allows specifying an effective period which is + * precise to fractions of a nanosecond, avoiding rounding errors. + */ void ptimer_set_freq(ptimer_state *s, uint32_t freq); + +/** + * ptimer_get_limit - Get the configured limit of the ptimer + * @s: ptimer to query + * + * This function returns the current limit (reload) value + * of the down-counter; that is, the value which it will be + * reset to when it hits zero. + * + * Generally timer devices using ptimers should be able to keep + * their reload register state inside the ptimer using the get + * and set limit functions rather than needing to also track it + * in their own state structure. + */ uint64_t ptimer_get_limit(ptimer_state *s); + +/** + * ptimer_set_limit - Set the limit of the ptimer + * @s: ptimer + * @limit: initial countdown value + * @reload: if nonzero, then reset the counter to the new limit + * + * Set the limit value of the down-counter. The @reload flag can + * be used to emulate the behaviour of timers which immediately + * reload the counter when their reload register is written to. + */ void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload); + +/** + * ptimer_get_count - Get the current value of the ptimer + * @s: ptimer + * + * Return the current value of the down-counter. This will + * return the correct value whether the counter is enabled or + * disabled. + */ uint64_t ptimer_get_count(ptimer_state *s); + +/** + * ptimer_set_count - Set the current value of the ptimer + * @s: ptimer + * @count: count value to set + * + * Set the value of the down-counter. If the counter is currently + * enabled this will arrange for a timer callback at the appropriate + * point in the future. + */ void ptimer_set_count(ptimer_state *s, uint64_t count); + +/** + * ptimer_run - Start a ptimer counting + * @s: ptimer + * @oneshot: non-zero if this timer should only count down once + * + * Start a ptimer counting down; when it reaches zero the bottom half + * passed to ptimer_init() will be invoked. If the @oneshot argument is zero, + * the counter value will then be reloaded from the limit and it will + * start counting down again. If @oneshot is non-zero, then the counter + * will disable itself when it reaches zero. + */ void ptimer_run(ptimer_state *s, int oneshot); + +/** + * ptimer_stop - Stop a ptimer counting + * @s: ptimer + * + * Pause a timer (the count stays at its current value until ptimer_run() + * is called to start it counting again). + * + * Note that this can cause it to "lose" time, even if it is immediately + * restarted. + */ void ptimer_stop(ptimer_state *s); extern const VMStateDescription vmstate_ptimer;