Tegra: spe: uninit console on a timeout

There are chances a denial-of-service attack, if an attacker
removes the SPE firmware from the system. The console driver
would end up waiting for the firmware to respond indefinitely.
The console driver must detect such scenarios and uninit the
interface as a result.

This patch adds a timeout to the interaction with the SPE
firmware and uninits the interface if it times out.

Change-Id: I06f27a858baed25711d41105b4110865f1a01727
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

plat/nvidia/tegra/common/drivers/spe/shared_console.S

 /*
  * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2020, NVIDIA Corporation. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -10,6 +11,7 @@
 #define CONSOLE_FLUSH_DATA_TO_PORT	(1 << 26)
 #define CONSOLE_RING_DOORBELL		(1 << 31)
 #define CONSOLE_IS_BUSY			(1 << 31)
+#define CONSOLE_TIMEOUT			0xC000		/* approx. 50 ms */
 #define CONSOLE_WRITE			(CONSOLE_RING_DOORBELL | CONSOLE_FLUSH_DATA_TO_PORT)
 
 	/*
@@ -30,6 +32,20 @@
 	.globl	console_spe_flush
 	.globl	console_spe_register
 
+.macro	check_if_console_is_ready base, tmp1, tmp2, label
+	/* wait until spe is ready or timeout expires */
+	mrs	\tmp2, cntps_tval_el1
+1:	ldr	\tmp1, [\base]
+	and	\tmp1, \tmp1, #CONSOLE_IS_BUSY
+	cbz	\tmp1, 2f
+	mrs	\tmp1, cntps_tval_el1
+	sub	\tmp1, \tmp2, \tmp1
+	cmp	\tmp1, #CONSOLE_TIMEOUT
+	b.lt	1b
+	b	\label
+2:
+.endm
+
 	/* -------------------------------------------------
 	 * int console_spe_register(uintptr_t baseaddr,
 	 *     uint32_t clock, uint32_t baud,
@@ -46,6 +62,12 @@
 	 * -------------------------------------------------
 	 */
 func console_spe_register
+	/* Check the input base address */
+	cbz	x0, register_fail
+
+	/* Dont use clock or baud rate, so ok to overwrite them */
+	check_if_console_is_ready x0, x1, x2, register_fail
+
 	cbz	x3, register_fail
 	str	x0, [x3, #CONSOLE_T_DRVDATA]
 	mov	x0, x3
@@ -63,7 +85,7 @@ endfunc console_spe_register
 	 * In : w0 - character to be printed
 	 *      x1 - console base address
 	 * Out : return -1 on error else return character.
-	 * Clobber list : x2
+	 * Clobber list : x2, x3
 	 * --------------------------------------------------------
 	 */
 func console_spe_core_putc
@@ -72,12 +94,9 @@ func console_spe_core_putc
 
 	/* Prepend '\r' to '\n' */
 	cmp	w0, #0xA
-	b.ne	2f
+	b.ne	not_eol
 
-	/* wait until spe is ready */
-1:	ldr	w2, [x1]
-	and	w2, w2, #CONSOLE_IS_BUSY
-	cbnz	w2, 1b
+	check_if_console_is_ready x1, x2, x3, putc_error
 
 	/* spe is ready */
 	mov	w2, #0xD		/* '\r' */
@@ -86,10 +105,8 @@ func console_spe_core_putc
 	orr	w2, w2, w3
 	str	w2, [x1]
 
-	/* wait until spe is ready */
-2:	ldr	w2, [x1]
-	and	w2, w2, #CONSOLE_IS_BUSY
-	cbnz	w2, 2b
+not_eol:
+	check_if_console_is_ready x1, x2, x3, putc_error
 
 	/* spe is ready */
 	mov	w2, w0