The present code does not wait for the SCC to finish resetting itself before trying to initialise the device. The result is that the SCC interrupt sources become enabled (if they weren't already). This leads to an early boot crash (unexpected interrupt) given CONFIG_EARLY_PRINTK. Fix this by adding a delay. A successful reset disables the interrupt sources. Also, after the reset for channel A setup, the SCC then gets a second reset for channel B setup which leaves channel A uninitialised again. Fix this by performing the reset only once. --- This patch can be applied to -stable trees >= 3.3.y. Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> Index: linux-3.3/arch/m68k/kernel/head.S =================================================================== --- linux-3.3.orig/arch/m68k/kernel/head.S 2013-05-28 21:28:52.000000000 +1000 +++ linux-3.3/arch/m68k/kernel/head.S 2013-05-28 21:37:33.000000000 +1000 @@ -2752,11 +2752,9 @@ func_return get_new_page #ifdef CONFIG_MAC L(scc_initable_mac): - .byte 9,12 /* Reset */ .byte 4,0x44 /* x16, 1 stopbit, no parity */ .byte 3,0xc0 /* receiver: 8 bpc */ .byte 5,0xe2 /* transmitter: 8 bpc, assert dtr/rts */ - .byte 9,0 /* no interrupts */ .byte 10,0 /* NRZ */ .byte 11,0x50 /* use baud rate generator */ .byte 12,1,13,0 /* 38400 baud */ @@ -2899,6 +2897,7 @@ func_start serial_init,%d0/%d1/%a0/%a1 is_not_mac(L(serial_init_not_mac)) #ifdef SERIAL_DEBUG + /* You may define either or both of these. */ #define MAC_USE_SCC_A /* Modem port */ #define MAC_USE_SCC_B /* Printer port */ @@ -2908,9 +2907,21 @@ func_start serial_init,%d0/%d1/%a0/%a1 #define mac_scc_cha_b_data_offset 0x4 #define mac_scc_cha_a_data_offset 0x6 +#if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B) + movel %pc@(L(mac_sccbase)),%a0 + /* Reset SCC device */ + moveb #9,%a0@(mac_scc_cha_a_ctrl_offset) + moveb #0xc0,%a0@(mac_scc_cha_a_ctrl_offset) + /* Wait for 5 PCLK cycles, which is about 68 CPU cycles */ + /* 5 / 3.6864 MHz = approx. 1.36 us = 68 / 50 MHz */ + movel #35,%d0 +5: + subq #1,%d0 + jne 5b +#endif + #ifdef MAC_USE_SCC_A /* Initialize channel A */ - movel %pc@(L(mac_sccbase)),%a0 lea %pc@(L(scc_initable_mac)),%a1 5: moveb %a1@+,%d0 jmi 6f @@ -2922,9 +2933,6 @@ func_start serial_init,%d0/%d1/%a0/%a1 #ifdef MAC_USE_SCC_B /* Initialize channel B */ -#ifndef MAC_USE_SCC_A /* Load mac_sccbase only if needed */ - movel %pc@(L(mac_sccbase)),%a0 -#endif /* MAC_USE_SCC_A */ lea %pc@(L(scc_initable_mac)),%a1 7: moveb %a1@+,%d0 jmi 8f @@ -2933,6 +2941,7 @@ func_start serial_init,%d0/%d1/%a0/%a1 jra 7b 8: #endif /* MAC_USE_SCC_B */ + #endif /* SERIAL_DEBUG */ jra L(serial_init_done) @@ -3006,17 +3015,17 @@ func_start serial_putc,%d0/%d1/%a0/%a1 #ifdef SERIAL_DEBUG -#ifdef MAC_USE_SCC_A +#if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B) movel %pc@(L(mac_sccbase)),%a1 +#endif + +#ifdef MAC_USE_SCC_A 3: btst #2,%a1@(mac_scc_cha_a_ctrl_offset) jeq 3b moveb %d0,%a1@(mac_scc_cha_a_data_offset) #endif /* MAC_USE_SCC_A */ #ifdef MAC_USE_SCC_B -#ifndef MAC_USE_SCC_A /* Load mac_sccbase only if needed */ - movel %pc@(L(mac_sccbase)),%a1 -#endif /* MAC_USE_SCC_A */ 4: btst #2,%a1@(mac_scc_cha_b_ctrl_offset) jeq 4b moveb %d0,%a1@(mac_scc_cha_b_data_offset) -- To unsubscribe from this list: send the line "unsubscribe linux-m68k" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
