HPET: Fix accessing HPET registers

This resolves a bochs panic during bootup:

[Kernel]: HPET @ P0x07ff0fc0
00691951632p[HPET  ] >>PANIC<< Unsupported HPET read at address 0x0000fed00100

These changes however don't fully resolve #2162

Kernel/Time/HPET.cpp

@@ -151,7 +151,7 @@ bool HPET::check_for_exisiting_periodic_timers()
 
     auto p_block = PhysicalAddress(sdt->event_timer_block.address);
     auto block_region = MM.allocate_kernel_region(p_block, (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
-    auto* registers = (HPETRegistersBlock*)block_region->vaddr().offset(p_block.offset_in_page()).as_ptr();
+    auto* registers = (volatile HPETRegistersBlock*)block_region->vaddr().offset(p_block.offset_in_page()).as_ptr();
 
     size_t timers_count = ((registers->raw_capabilites.reg >> 8) & 0x1f) + 1;
     for (size_t index = 0; index < timers_count; index++) {
@@ -163,13 +163,13 @@ bool HPET::check_for_exisiting_periodic_timers()
 
 void HPET::global_disable()
 {
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    registers_block->configuration.reg &= ~(u32)HPETFlags::Configuration::Enable;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->configuration.reg = registers_block->configuration.reg & ~(u32)HPETFlags::Configuration::Enable;
 }
 void HPET::global_enable()
 {
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    registers_block->configuration.reg |= (u32)HPETFlags::Configuration::Enable;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->configuration.reg = registers_block->configuration.reg | (u32)HPETFlags::Configuration::Enable;
 }
 
 void HPET::set_periodic_comparator_value(const HPETComparator& comparator, u64 value)
@@ -177,9 +177,10 @@ void HPET::set_periodic_comparator_value(const HPETComparator& comparator, u64 v
     disable(comparator);
     ASSERT(comparator.is_periodic());
     ASSERT(comparator.comparator_number() <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    registers_block->timers[comparator.comparator_number()].configuration_and_capability |= (u32)HPETFlags::TimerConfiguration::ValueSet;
-    registers_block->timers[comparator.comparator_number()].comparator_value = value;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    volatile auto* timer = &registers_block->timers[comparator.comparator_number()];
+    timer->configuration_and_capability = timer->configuration_and_capability | (u32)HPETFlags::TimerConfiguration::ValueSet;
+    timer->comparator_value = value;
     enable(comparator);
 }
 
@@ -188,7 +189,7 @@ void HPET::set_non_periodic_comparator_value(const HPETComparator& comparator, u
     ASSERT_INTERRUPTS_DISABLED();
     ASSERT(!comparator.is_periodic());
     ASSERT(comparator.comparator_number() <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
     registers_block->timers[comparator.comparator_number()].comparator_value = main_counter_value() + value;
 }
 void HPET::enable_periodic_interrupt(const HPETComparator& comparator)
@@ -198,9 +199,11 @@ void HPET::enable_periodic_interrupt(const HPETComparator& comparator)
 #endif
     disable(comparator);
     ASSERT(comparator.comparator_number() <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    ASSERT(registers_block->timers[comparator.comparator_number()].configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable);
-    registers_block->timers[comparator.comparator_number()].configuration_and_capability |= (u32)HPETFlags::TimerConfiguration::TimerType;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    volatile auto* timer = &registers_block->timers[comparator.comparator_number()];
+    auto configuration_and_capability = timer->configuration_and_capability;
+    ASSERT(configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable);
+    timer->configuration_and_capability = configuration_and_capability | (u32)HPETFlags::TimerConfiguration::TimerType;
     enable(comparator);
 }
 void HPET::disable_periodic_interrupt(const HPETComparator& comparator)
@@ -210,9 +213,11 @@ void HPET::disable_periodic_interrupt(const HPETComparator& comparator)
 #endif
     disable(comparator);
     ASSERT(comparator.comparator_number() <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    ASSERT(registers_block->timers[comparator.comparator_number()].configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable);
-    registers_block->timers[comparator.comparator_number()].configuration_and_capability &= ~(u32)HPETFlags::TimerConfiguration::TimerType;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto volatile* timer = &registers_block->timers[comparator.comparator_number()];
+    auto configuration_and_capability = timer->configuration_and_capability;
+    ASSERT(configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable);
+    timer->configuration_and_capability = configuration_and_capability & ~(u32)HPETFlags::TimerConfiguration::TimerType;
     enable(comparator);
 }
 
@@ -222,8 +227,9 @@ void HPET::disable(const HPETComparator& comparator)
     klog() << "HPET: Disable comparator " << comparator.comparator_number() << ".";
 #endif
     ASSERT(comparator.comparator_number() <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    registers_block->timers[comparator.comparator_number()].configuration_and_capability &= ~(u32)HPETFlags::TimerConfiguration::InterruptEnable;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    volatile auto* timer = &registers_block->timers[comparator.comparator_number()];
+    timer->configuration_and_capability = timer->configuration_and_capability & ~(u32)HPETFlags::TimerConfiguration::InterruptEnable;
 }
 void HPET::enable(const HPETComparator& comparator)
 {
@@ -231,13 +237,14 @@ void HPET::enable(const HPETComparator& comparator)
     klog() << "HPET: Enable comparator " << comparator.comparator_number() << ".";
 #endif
     ASSERT(comparator.comparator_number() <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    registers_block->timers[comparator.comparator_number()].configuration_and_capability |= (u32)HPETFlags::TimerConfiguration::InterruptEnable;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    volatile auto* timer = &registers_block->timers[comparator.comparator_number()];
+    timer->configuration_and_capability = timer->configuration_and_capability | (u32)HPETFlags::TimerConfiguration::InterruptEnable;
 }
 
 u64 HPET::main_counter_value() const
 {
-    auto* registers_block = (const HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* registers_block = (const volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
     return registers_block->main_counter_value.reg;
 }
 u64 HPET::frequency() const
@@ -249,8 +256,8 @@ Vector<unsigned> HPET::capable_interrupt_numbers(const HPETComparator& comparato
 {
     ASSERT(comparator.comparator_number() <= m_comparators.size());
     Vector<unsigned> capable_interrupts;
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    auto* comparator_registers = (const TimerStructure*)&registers_block->timers[comparator.comparator_number()];
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (const volatile TimerStructure*)&registers_block->timers[comparator.comparator_number()];
     u32 interrupt_bitfield = comparator_registers->configuration_and_capability >> 32;
     for (size_t index = 0; index < 32; index++) {
         if (interrupt_bitfield & 1)
@@ -264,8 +271,8 @@ Vector<unsigned> HPET::capable_interrupt_numbers(u8 comparator_number)
 {
     ASSERT(comparator_number <= m_comparators.size());
     Vector<unsigned> capable_interrupts;
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    auto* comparator_registers = (const TimerStructure*)&registers_block->timers[comparator_number];
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (const volatile TimerStructure*)&registers_block->timers[comparator_number];
     u32 interrupt_bitfield = comparator_registers->configuration_and_capability >> 32;
     for (size_t index = 0; index < 32; index++) {
         if (interrupt_bitfield & 1)
@@ -278,16 +285,16 @@ Vector<unsigned> HPET::capable_interrupt_numbers(u8 comparator_number)
 void HPET::set_comparator_irq_vector(u8 comparator_number, u8 irq_vector)
 {
     ASSERT(comparator_number <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    auto* comparator_registers = (TimerStructure*)&registers_block->timers[comparator_number];
-    comparator_registers->configuration_and_capability |= (irq_vector << 9);
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (volatile TimerStructure*)&registers_block->timers[comparator_number];
+    comparator_registers->configuration_and_capability = comparator_registers->configuration_and_capability | (irq_vector << 9);
 }
 
 bool HPET::is_periodic_capable(u8 comparator_number) const
 {
     ASSERT(comparator_number <= m_comparators.size());
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
-    auto* comparator_registers = (const TimerStructure*)&registers_block->timers[comparator_number];
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (const volatile TimerStructure*)&registers_block->timers[comparator_number];
     return comparator_registers->configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable;
 }
 
@@ -300,13 +307,13 @@ void HPET::set_comparators_to_optimal_interrupt_state(size_t)
 PhysicalAddress HPET::find_acpi_hept_registers_block()
 {
     auto region = MM.allocate_kernel_region(m_physical_acpi_hpet_table.page_base(), (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
-    auto* sdt = (ACPI::Structures::HPET*)region->vaddr().offset(m_physical_acpi_hpet_table.offset_in_page()).as_ptr();
+    auto* sdt = (const volatile ACPI::Structures::HPET*)region->vaddr().offset(m_physical_acpi_hpet_table.offset_in_page()).as_ptr();
     ASSERT(sdt->event_timer_block.address_space == (u8)ACPI::GenericAddressStructure::AddressSpace::SystemMemory);
     return PhysicalAddress(sdt->event_timer_block.address);
 }
 u64 HPET::calculate_ticks_in_nanoseconds() const
 {
-    auto* registers_block = (const HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* registers_block = (const volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
     return ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD / registers_block->capabilities.main_counter_tick_period;
 }
 HPET::HPET(PhysicalAddress acpi_hpet)
@@ -315,18 +322,18 @@ HPET::HPET(PhysicalAddress acpi_hpet)
     , m_hpet_mmio_region(MM.allocate_kernel_region(m_physical_acpi_hpet_registers.page_base(), PAGE_SIZE, "HPET MMIO", Region::Access::Read | Region::Access::Write))
 {
     auto region = MM.allocate_kernel_region(m_physical_acpi_hpet_table.page_base(), (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
-    auto* sdt = (ACPI::Structures::HPET*)region->vaddr().offset(m_physical_acpi_hpet_table.offset_in_page()).as_ptr();
+    auto* sdt = (const volatile ACPI::Structures::HPET*)region->vaddr().offset(m_physical_acpi_hpet_table.offset_in_page()).as_ptr();
     m_vendor_id = sdt->pci_vendor_id;
     m_minimum_tick = sdt->mininum_clock_tick;
     klog() << "HPET: Minimum clock tick - " << m_minimum_tick;
 
-    auto* registers_block = (HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
 
     // Note: We must do a 32 bit access to offsets 0x0, or 0x4 only.
     size_t timers_count = ((registers_block->raw_capabilites.reg >> 8) & 0x1f) + 1;
     klog() << "HPET: Timers count - " << timers_count;
     ASSERT(timers_count >= 2);
-    auto* capabilities_register = (const HPETCapabilityRegister*)&registers_block->raw_capabilites.reg;
+    auto* capabilities_register = (const volatile HPETCapabilityRegister*)&registers_block->raw_capabilites.reg;
 
     global_disable();
 
@@ -337,7 +344,7 @@ HPET::HPET(PhysicalAddress acpi_hpet)
     // Reset the counter, just in case...
     registers_block->main_counter_value.reg = 0;
     if (registers_block->raw_capabilites.reg & (u32)HPETFlags::Attributes::LegacyReplacementRouteCapable)
-        registers_block->configuration.reg |= (u32)HPETFlags::Configuration::LegacyReplacementRoute;
+        registers_block->configuration.reg = registers_block->configuration.reg | (u32)HPETFlags::Configuration::LegacyReplacementRoute;
 
     m_comparators.append(HPETComparator::create(0, 0, is_periodic_capable(0)));
     m_comparators.append(HPETComparator::create(1, 8, is_periodic_capable(1)));