fix(regression): freeze with multiple NVMe devices

Removing the PCI status bit check in the interrupt handler caused the
code to break and not work if there was more than one NVMe device
successfully attached. Not only does this commit fix this issue, but
this also adds a proper check to see if the device generated an
interrupt by checking if any commands have been posted to the completion
queue.

drivers/nvme/nvme.asm

@@ -76,7 +76,7 @@ local   AnythingLoadedSuccessfully db 0
 	test 	eax, eax
 	setne	[AnythingLoadedSuccessfully]
 	inc 	ebx
-	cmp 	ebx, dword [pcidevs_len]
+	cmp 	ebx, dword [num_pcidevs]
 	jne 	.loop
 	cmp 	[AnythingLoadedSuccessfully], 0
 	jz 	.err
@@ -536,7 +536,7 @@ proc nvme_readwrite stdcall, ns:dword, buf:dword, start_sector:qword, numsectors
 endp
 
 ; Detects NVMe devices on the PCI bus and stores them into 
-; [p_nvme_devices] and sets [pcidevs_len] to the appropriate
+; [p_nvme_devices] and sets [num_pcidevs] to the appropriate
 ; size based off how many NVMe devices there are.
 proc detect_nvme
 
@@ -571,13 +571,14 @@ proc detect_nvme
 	jnz 	.err
 
 @@:
-	cmp 	dword [pcidevs_len], TOTAL_PCIDEVS
+	cmp 	dword [num_pcidevs], TOTAL_PCIDEVS
 	jne 	@f
 	DEBUGF  DBG_INFO, "Can't add any more NVMe devices...\n"
 	jmp 	.exit_success
 
 @@:
-	inc 	dword [pcidevs_len]
+	inc 	dword [num_pcidevs]
+	add 	dword [num_pcidevs_sz], sizeof.pcidev
 	cmp     dword [p_nvme_devices], 0
 	jnz	@f ; was the pointer already allocated?
 	invoke  KernelAlloc, sizeof.pcidev * TOTAL_PCIDEVS
@@ -588,7 +589,7 @@ proc detect_nvme
 	DEBUGF  DBG_INFO, "nvme: Allocated memory for PCI devices at: 0x%x\n", eax
 
 @@:
-	mov 	ecx, dword [pcidevs_len]
+	mov 	ecx, dword [num_pcidevs]
 	dec 	ecx
 	mov 	edi, dword [p_nvme_devices]
 	mov 	edx, ecx
@@ -1281,19 +1282,24 @@ endp
 proc irq_handler
 
 	push 	ebx esi edi
-	mov 	edi, dword [p_nvme_devices]
+	mov 	esi, dword [p_nvme_devices]
-	mov 	esi, edi
+	mov 	ebx, dword [num_pcidevs_sz]
-	sub 	esi, sizeof.pcidev
+	add 	ebx, esi
-	mov 	ebx, dword [pcidevs_len]
-	xor 	ecx, ecx
 
 .check_who_raised_irq:
+	stdcall device_generated_interrupt, esi
+	test 	eax, eax
+	jnz 	@f
 	add 	esi, sizeof.pcidev
-	inc 	ecx
+	cmp 	esi, ebx
-	cmp 	ecx, ebx
+	jbe 	.check_who_raised_irq
-	; TODO: Apply solution given by @punk_joker of checking which device 
+
-	; generated an interrupt.
+	; Interrupt not handled by driver, return 0
-	ja 	.not_our_irq
+	pop 	edi esi ebx
+	xor 	eax, eax
+	ret
+
+@@:
 	mov 	edi, dword [esi + pcidev.io_addr]
 	mov 	dword [edi + NVME_MMIO.INTMS], 0x3
 	stdcall consume_cq_entries, esi, ADMIN_QUEUE
@@ -1307,12 +1313,28 @@ proc irq_handler
 	mov 	eax, 1
 	ret
 
-.not_our_irq:
+endp
-	; Interrupt not handled by driver, return 0
+
-	pop 	edi esi ebx
+proc device_generated_interrupt stdcall, pci:dword
+
+	mov 	edx, [pci]
+	mov 	edx, dword [edx + pcidev.queue_entries]
+	xor 	ecx, ecx
+
+@@:
+	mov 	ax, word [edx + ecx + NVM_QUEUE_ENTRY.head]
+	cmp 	ax, word [edx + ecx + NVM_QUEUE_ENTRY.tail]
+	jne 	@f
+	add 	ecx, sizeof.NVM_QUEUE_ENTRY
+	cmp 	ecx, LAST_QUEUE_ID * sizeof.NVM_QUEUE_ENTRY
+	jbe 	@b
 	xor 	eax, eax
 	ret
 
+@@:
+	mov 	eax, 1
+	ret
+
 endp
 
 ; Deletes the allocated I/O queues for all of the NVMe devices,
@@ -1363,7 +1385,7 @@ proc nvme_cleanup
 	jbe 	.get_queue
 	pop 	ebx
 	inc 	ebx
-	cmp 	ebx, dword [pcidevs_len]
+	cmp 	ebx, dword [num_pcidevs]
 	jne 	.get_pcidev
 
 	; NOTE: This code has a bug! It only shuts down the last
@@ -1390,8 +1412,9 @@ endp
 
 ;all initialized data place here
 align 4
-	p_nvme_devices dd 0
+	p_nvme_devices dd 0 ; Pointer to array of NVMe devices
-	pcidevs_len  dd 0
+	num_pcidevs    dd 0 ; Number of NVMe devices
+	num_pcidevs_sz dd 0 ; Size in bytes
 	my_service   db "nvme",0  ;max 16 chars include zero
 	disk_functions:
 		dd 	 disk_functions.end - disk_functions