malta: enable PIIX4 SERIRQ

Whilst U-boot does not require this itself, Linux currently relies upon
it having been muxed and enabled by the bootloader. Thus in order to
preserve compatibility with current kernels before a fix is merged in
Linux we will enable the SERIRQ interrupt and mux it to its pin.

Without doing this current kernels will never receive serial port
interrupts and the end result is typically that userland appears to
hang.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>

arch/mips/include/asm/malta.h

@@ -56,5 +56,12 @@
 #define PCI_CFG_PIIX4_PIRQRCB		0x61
 #define PCI_CFG_PIIX4_PIRQRCC		0x62
 #define PCI_CFG_PIIX4_PIRQRCD		0x63
+#define PCI_CFG_PIIX4_SERIRQC		0x64
+#define PCI_CFG_PIIX4_GENCFG		0xb0
+
+#define PCI_CFG_PIIX4_SERIRQC_EN	(1 << 7)
+#define PCI_CFG_PIIX4_SERIRQC_CONT	(1 << 6)
+
+#define PCI_CFG_PIIX4_GENCFG_SERIRQ	(1 << 16)
 
 #endif /* _MIPS_ASM_MALTA_H */

board/imgtec/malta/malta.c

@@ -171,6 +171,8 @@ struct serial_device *default_serial_console(void)
 void pci_init_board(void)
 {
 	pci_dev_t bdf;
+	u32 val32;
+	u8 val8;
 
 	switch (malta_sys_con()) {
 	case SYSCON_GT64120:
@@ -205,4 +207,14 @@ void pci_init_board(void)
 	pci_write_config_byte(bdf, PCI_CFG_PIIX4_PIRQRCB, 10);
 	pci_write_config_byte(bdf, PCI_CFG_PIIX4_PIRQRCC, 11);
 	pci_write_config_byte(bdf, PCI_CFG_PIIX4_PIRQRCD, 11);
+
+	/* mux SERIRQ onto SERIRQ pin */
+	pci_read_config_dword(bdf, PCI_CFG_PIIX4_GENCFG, &val32);
+	val32 |= PCI_CFG_PIIX4_GENCFG_SERIRQ;
+	pci_write_config_dword(bdf, PCI_CFG_PIIX4_GENCFG, val32);
+
+	/* enable SERIRQ - Linux currently depends upon this */
+	pci_read_config_byte(bdf, PCI_CFG_PIIX4_SERIRQC, &val8);
+	val8 |= PCI_CFG_PIIX4_SERIRQC_EN | PCI_CFG_PIIX4_SERIRQC_CONT;
+	pci_write_config_byte(bdf, PCI_CFG_PIIX4_SERIRQC, val8);
 }