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xen.21118
60787714-x86-HPET-factor-legacy-replacement-mod...
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File 60787714-x86-HPET-factor-legacy-replacement-mode-enabling.patch of Package xen.21118
# Commit 238168b5bcd27fec97704f6295fa5bf7a442eb6f # Date 2021-04-15 18:25:40 +0100 # Author Andrew Cooper <andrew.cooper3@citrix.com> # Committer Andrew Cooper <andrew.cooper3@citrix.com> x86/hpet: Factor hpet_enable_legacy_replacement_mode() out of hpet_setup() ... in preparation to introduce a second caller. No functional change. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com> Tested-by: Frédéric Pierret <frederic.pierret@qubes-os.org> --- a/xen/arch/x86/hpet.c +++ b/xen/arch/x86/hpet.c @@ -762,11 +762,70 @@ int hpet_legacy_irq_tick(void) } static u32 *hpet_boot_cfg; +static uint64_t __initdata hpet_rate; + +bool __init hpet_enable_legacy_replacement_mode(void) +{ + unsigned int cfg, c0_cfg, ticks, count; + + if ( !hpet_rate || + !(hpet_read32(HPET_ID) & HPET_ID_LEGSUP) || + ((cfg = hpet_read32(HPET_CFG)) & HPET_CFG_LEGACY) ) + return false; + + /* Stop the main counter. */ + hpet_write32(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(cfg | HPET_CFG_ENABLE | HPET_CFG_LEGACY, HPET_CFG); + + return true; +} u64 __init hpet_setup(void) { - static u64 __initdata hpet_rate; - unsigned int hpet_id, hpet_period, hpet_cfg; + unsigned int hpet_id, hpet_period; unsigned int last; if ( hpet_rate ) @@ -811,58 +870,7 @@ u64 __init hpet_setup(void) * 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); - } + hpet_enable_legacy_replacement_mode(); return hpet_rate; } --- a/xen/include/asm-x86/hpet.h +++ b/xen/include/asm-x86/hpet.h @@ -73,6 +73,12 @@ void hpet_disable(void); int hpet_legacy_irq_tick(void); /* + * Try to enable HPET Legacy Replacement mode. Returns a boolean indicating + * whether the HPET configuration was changed. + */ +bool hpet_enable_legacy_replacement_mode(void); + +/* * Temporarily use an HPET event counter for timer interrupt handling, * rather than using the LAPIC timer. Used for Cx state entry. */
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