diff --git a/xen/arch/x86/hpet.c b/xen/arch/x86/hpet.c index 86b4e88f9b..e99d7116b6 100644 --- a/xen/arch/x86/hpet.c +++ b/xen/arch/x86/hpet.c @@ -767,7 +767,7 @@ static u32 *hpet_boot_cfg; u64 __init hpet_setup(void) { static u64 __initdata hpet_rate; - unsigned int hpet_id, hpet_period, hpet_cfg; + u32 hpet_id, hpet_period; unsigned int last; if ( hpet_rate ) @@ -800,71 +800,6 @@ u64 __init hpet_setup(void) hpet_rate = 1000000000000000ULL; /* 10^15 */ (void)do_div(hpet_rate, hpet_period); - /* - * Intel chipsets from Skylake/ApolloLake onwards can statically clock - * gate the 8259 PIT. This option is enabled by default in slightly later - * systems, as turning the PIT off is a prerequisite to entering the C11 - * power saving state. - * - * Xen currently depends on the legacy timer interrupt being active while - * IRQ routing is configured. - * - * Reconfigure the HPET into legacy mode to re-establish the timer - * interrupt. - */ - if ( hpet_id & HPET_ID_LEGSUP && - !((hpet_cfg = hpet_read32(HPET_CFG)) & HPET_CFG_LEGACY) ) - { - unsigned int c0_cfg, ticks, count; - - /* Stop the main counter. */ - hpet_write32(hpet_cfg & ~HPET_CFG_ENABLE, HPET_CFG); - - /* Reconfigure channel 0 to be 32bit periodic. */ - c0_cfg = hpet_read32(HPET_Tn_CFG(0)); - c0_cfg |= (HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL | - HPET_TN_32BIT); - hpet_write32(c0_cfg, HPET_Tn_CFG(0)); - - /* - * The exact period doesn't have to match a legacy PIT. All we need - * is an interrupt queued up via the IO-APIC to check routing. - * - * Use HZ as the frequency. - */ - ticks = ((SECONDS(1) / HZ) * div_sc(hpet_rate, SECONDS(1), 32)) >> 32; - - count = hpet_read32(HPET_COUNTER); - - /* - * HPET_TN_SETVAL above is atrociously documented in the spec. - * - * Periodic HPET channels have a main comparator register, and - * separate "accumulator" register. Despite being named accumulator - * in the spec, this is not an accurate description of its behaviour - * or purpose. - * - * Each time an interrupt is generated, the "accumulator" register is - * re-added to the comparator set up the new period. - * - * Normally, writes to the CMP register update both registers. - * However, under these semantics, it is impossible to set up a - * periodic timer correctly without the main HPET counter being at 0. - * - * Instead, HPET_TN_SETVAL is a self-clearing control bit which we can - * use for periodic timers to mean that the second write to CMP - * updates the accumulator only, and not the absolute comparator - * value. - * - * This lets us set a period when the main counter isn't at 0. - */ - hpet_write32(count + ticks, HPET_Tn_CMP(0)); - hpet_write32(ticks, HPET_Tn_CMP(0)); - - /* Restart the main counter, and legacy mode. */ - hpet_write32(hpet_cfg | HPET_CFG_ENABLE | HPET_CFG_LEGACY, HPET_CFG); - } - return hpet_rate; }