[intel] Force RX polling on VMware emulated 82545em

The emulated Intel 82545em in some versions of VMware (observed with
ESXi v5.1) seems to sometimes fail to set the RXT0 bit in the
interrupt cause register (ICR), causing iPXE to stop receiving
packets.  Work around this problem (for the 82545em only) by always
polling the receive queue regardless of the state of the ICR.

Reported-by: Slava Bendersky <volga629@networklab.ca>
Tested-by: Slava Bendersky <volga629@networklab.ca>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/intel.c

 	/* Update link state */
 	intel_check_link ( netdev );
 
+	/* Apply required errata */
+	if ( intel->flags & INTEL_VMWARE ) {
+		DBGC ( intel, "INTEL %p applying VMware errata workaround\n",
+		       intel );
+		intel->force_icr = INTEL_IRQ_RXT0;
+	}
+
 	return 0;
 
 	intel_destroy_ring ( intel, &intel->rx );
 	icr = readl ( intel->regs + INTEL_ICR );
 	profile_stop ( &intel_vm_poll_profiler );
 	profile_exclude ( &intel_vm_poll_profiler );
+	icr |= intel->force_icr;
 	if ( ! icr )
 		return;
 
 	PCI_ROM ( 0x8086, 0x100c, "82544gc", "82544GC (Copper)", 0 ),
 	PCI_ROM ( 0x8086, 0x100d, "82544gc-l", "82544GC (LOM)", 0 ),
 	PCI_ROM ( 0x8086, 0x100e, "82540em", "82540EM", 0 ),
-	PCI_ROM ( 0x8086, 0x100f, "82545em", "82545EM (Copper)", 0 ),
+	PCI_ROM ( 0x8086, 0x100f, "82545em", "82545EM (Copper)", INTEL_VMWARE ),
 	PCI_ROM ( 0x8086, 0x1010, "82546eb", "82546EB (Copper)", 0 ),
 	PCI_ROM ( 0x8086, 0x1011, "82545em-f", "82545EM (Fiber)", 0 ),
 	PCI_ROM ( 0x8086, 0x1012, "82546eb-f", "82546EB (Fiber)", 0 ),

src/drivers/net/intel.h

 	unsigned int port;
 	/** Flags */
 	unsigned int flags;
+	/** Forced interrupts */
+	unsigned int force_icr;
 
 	/** EEPROM */
 	struct nvs_device eeprom;
 enum intel_flags {
 	/** PBS/PBA errata workaround required */
 	INTEL_PBS_ERRATA = 0x0001,
+	/** VMware missing interrupt workaround required */
+	INTEL_VMWARE = 0x0002,
 };
 
 extern int intel_create_ring ( struct intel_nic *intel,