From 1c1fc65c7cf78aefcd88b951eb7ca478d83fe0a8 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Tue, 1 Apr 2025 22:55:05 +0300
Subject: [PATCH] Kernel: Add API to reserve GSI instead of irq

This also fixes a bug with IOAPIC gsi_base != 0
---
 kernel/include/kernel/APIC.h |  2 ++
 kernel/kernel/APIC.cpp       | 52 +++++++++++++++++++++++++++---------
 2 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/kernel/include/kernel/APIC.h b/kernel/include/kernel/APIC.h
index 2054be6b..194e1689 100644
--- a/kernel/include/kernel/APIC.h
+++ b/kernel/include/kernel/APIC.h
@@ -23,6 +23,8 @@ namespace Kernel
 		virtual void broadcast_ipi() override;
 		virtual void enable() override;
 
+		BAN::ErrorOr<uint8_t> reserve_gsi(uint32_t gsi);
+
 		void initialize_timer();
 
 	private:
diff --git a/kernel/kernel/APIC.cpp b/kernel/kernel/APIC.cpp
index a847fac9..7e1a832e 100644
--- a/kernel/kernel/APIC.cpp
+++ b/kernel/kernel/APIC.cpp
@@ -458,7 +458,7 @@ namespace Kernel
 	{
 		SpinLockGuard _(m_lock);
 
-		uint32_t gsi = m_irq_overrides[irq];
+		const uint32_t gsi = m_irq_overrides[irq];
 
 		{
 			int byte = gsi / 8;
@@ -477,9 +477,11 @@ namespace Kernel
 		}
 		ASSERT(ioapic);
 
+		const uint32_t pin = gsi - ioapic->gsi_base;
+
 		RedirectionEntry redir;
-		redir.lo_dword = ioapic->read(IOAPIC_REDIRS + gsi * 2);
-		redir.hi_dword = ioapic->read(IOAPIC_REDIRS + gsi * 2 + 1);
+		redir.lo_dword = ioapic->read(IOAPIC_REDIRS + pin * 2);
+		redir.hi_dword = ioapic->read(IOAPIC_REDIRS + pin * 2 + 1);
 		ASSERT(redir.mask); // TODO: handle overlapping interrupts
 
 		redir.vector = IRQ_VECTOR_BASE + irq;
@@ -487,8 +489,8 @@ namespace Kernel
 		// FIXME: distribute IRQs more evenly?
 		redir.destination = Kernel::Processor::bsb_id().as_u32();
 
-		ioapic->write(IOAPIC_REDIRS + gsi * 2,		redir.lo_dword);
-		ioapic->write(IOAPIC_REDIRS + gsi * 2 + 1,	redir.hi_dword);
+		ioapic->write(IOAPIC_REDIRS + pin * 2,		redir.lo_dword);
+		ioapic->write(IOAPIC_REDIRS + pin * 2 + 1,	redir.hi_dword);
 	}
 
 	bool APIC::is_in_service(uint8_t irq)
@@ -504,35 +506,59 @@ namespace Kernel
 	{
 		SpinLockGuard _(m_lock);
 
-		uint32_t gsi = m_irq_overrides[irq];
+		const uint32_t gsi = m_irq_overrides[irq];
 
-		IOAPIC* ioapic = nullptr;
-		for (IOAPIC& io : m_io_apics)
+		bool found_ioapic = false;
+		for (const auto& io : m_io_apics)
 		{
 			if (io.gsi_base <= gsi && gsi <= io.gsi_base + io.max_redirs)
 			{
-				ioapic = &io;
+				found_ioapic = true;
 				break;
 			}
 		}
 
-		if (!ioapic)
+		if (!found_ioapic)
 		{
-			dwarnln("Cannot enable irq {} for APIC", irq);
-			return BAN::Error::from_errno(EFAULT);
+			dwarnln("No IOAPIC for GSI {}", gsi);
+			return BAN::Error::from_errno(EINVAL);
 		}
 
 		int byte = gsi / 8;
 		int bit  = gsi % 8;
 		if (m_reserved_gsis[byte] & (1 << bit))
 		{
-			dwarnln("irq {} is already reserved", irq);
+			dwarnln("GSI {} is already reserved", gsi);
 			return BAN::Error::from_errno(EFAULT);
 		}
 		m_reserved_gsis[byte] |= 1 << bit;
 		return {};
 	}
 
+	// FIXME: rewrite gsi and vector reserving
+	//        this is a hack to allow direct GSI reservation
+	BAN::ErrorOr<uint8_t> APIC::reserve_gsi(uint32_t gsi)
+	{
+		dwarnln("TRYING TO RESERVE GSI {}", gsi);
+
+		size_t irq = 0;
+		for (; irq < 0x100; irq++)
+			if (m_irq_overrides[irq] == gsi)
+				break;
+
+		if (irq == 0x100)
+		{
+			dwarnln("TODO: reserve GSI not accessible through overrides");
+			return BAN::Error::from_errno(ENOTSUP);
+		}
+
+		dwarnln("  matches IRQ {}", irq);
+
+		TRY(reserve_irq(irq));
+
+		return irq;
+	}
+
 	BAN::Optional<uint8_t> APIC::get_free_irq()
 	{
 		SpinLockGuard _(m_lock);