[time] Add support for the ACPI power management timer

Allow the ACPI power management timer to be used if enabled via
TIMER_ACPI in config/timer.h.  This provides an alternative timer on
systems where the standard 8254 PIT is unavailable or unreliable.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/interface/pcbios/acpi_timer.c

@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) 2018 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <unistd.h>
+#include <errno.h>
+#include <assert.h>
+#include <byteswap.h>
+#include <ipxe/io.h>
+#include <ipxe/acpi.h>
+
+/** @file
+ *
+ * ACPI power management timer
+ *
+ */
+
+/** ACPI timer frequency (fixed 3.579545MHz) */
+#define ACPI_TIMER_HZ 3579545
+
+/** ACPI timer mask
+ *
+ * Timers may be implemented as either 24-bit or 32-bit counters.  We
+ * simplify the code by pessimistically assuming that the timer has
+ * only 24 bits.
+ */
+#define ACPI_TIMER_MASK 0x00ffffffUL
+
+/** Power management timer register address */
+static unsigned int pm_tmr;
+
+struct timer acpi_timer __timer ( TIMER_PREFERRED );
+
+/**
+ * Get current system time in ticks
+ *
+ * @ret ticks		Current time, in ticks
+ */
+static unsigned long acpi_currticks ( void ) {
+	static unsigned long offset;
+	static uint32_t prev;
+	uint32_t now;
+
+	/* Read timer and account for wraparound */
+	now = ( inl ( pm_tmr ) & ACPI_TIMER_MASK );
+	if ( now < prev ) {
+		offset += ( ( ACPI_TIMER_MASK + 1 ) /
+			    ( ACPI_TIMER_HZ / TICKS_PER_SEC ) );
+	}
+	prev = now;
+
+	/* Convert to timer ticks */
+	return ( offset + ( now / ( ACPI_TIMER_HZ / TICKS_PER_SEC ) ) );
+}
+
+/**
+ * Delay for a fixed number of microseconds
+ *
+ * @v usecs		Number of microseconds for which to delay
+ */
+static void acpi_udelay ( unsigned long usecs ) {
+	uint32_t start;
+	uint32_t elapsed;
+	uint32_t threshold;
+
+	/* Delay until a suitable number of ticks have elapsed.  We do
+	 * not need to allow for multiple wraparound, since the
+	 * wraparound period for a 24-bit timer at 3.579545MHz is
+	 * around 4700000us.
+	 */
+	start = inl ( pm_tmr );
+	threshold = ( ( usecs * ACPI_TIMER_HZ ) / 1000000 );
+	do {
+		elapsed = ( ( inl ( pm_tmr ) - start ) & ACPI_TIMER_MASK );
+	} while ( elapsed < threshold );
+}
+
+/**
+ * Probe ACPI power management timer
+ *
+ * @ret rc		Return status code
+ */
+static int acpi_timer_probe ( void ) {
+	struct acpi_fadt fadtab;
+	userptr_t fadt;
+	unsigned int pm_tmr_blk;
+
+	/* Locate FADT */
+	fadt = acpi_find ( FADT_SIGNATURE, 0 );
+	if ( ! fadt ) {
+		DBGC ( &acpi_timer, "ACPI could not find FADT\n" );
+		return -ENOENT;
+	}
+
+	/* Read FADT */
+	copy_from_user ( &fadtab, fadt, 0, sizeof ( fadtab ) );
+	pm_tmr_blk = le32_to_cpu ( fadtab.pm_tmr_blk );
+	if ( ! pm_tmr_blk ) {
+		DBGC ( &acpi_timer, "ACPI has no timer\n" );
+		return -ENOENT;
+	}
+
+	/* Record power management timer register address */
+	pm_tmr = ( pm_tmr_blk + ACPI_PM_TMR );
+
+	return 0;
+}
+
+/** ACPI timer */
+struct timer acpi_timer __timer ( TIMER_PREFERRED ) = {
+	.name = "acpi",
+	.probe = acpi_timer_probe,
+	.currticks = acpi_currticks,
+	.udelay = acpi_udelay,
+};