ARM: stm32: debug: add low-level debug support

This adds low-level debug support on USART1 for STM32F4
and STM32F7.
Compiled via 'CONFIG_DEBUG_LL' and 'CONFIG_EARLY_PRINTK'.
Enabled via 'earlyprintk' in bootargs.

Signed-off-by: Gerald Baeza <gerald.baeza@st.com>
Signed-off-by: Bich Hemon <bich.hemon@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index d6a49f5..672147e 100644 (file)
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -1192,6 +1192,28 @@ choice
 
                  If unsure, say N.
 
+       config STM32F4_DEBUG_UART
+               bool "Use STM32F4 UART for low-level debug"
+               depends on ARCH_STM32
+               select DEBUG_STM32_UART
+               help
+                 Say Y here if you want kernel low-level debugging support
+                 on STM32F4 based platforms, which default UART is wired on
+                 USART1.
+
+                 If unsure, say N.
+
+       config STM32F7_DEBUG_UART
+               bool "Use STM32F7 UART for low-level debug"
+               depends on ARCH_STM32
+               select DEBUG_STM32_UART
+               help
+                 Say Y here if you want kernel low-level debugging support
+                 on STM32F7 based platforms, which default UART is wired on
+                 USART1.
+
+                 If unsure, say N.
+
        config TEGRA_DEBUG_UART_AUTO_ODMDATA
                bool "Kernel low-level debugging messages via Tegra UART via ODMDATA"
                depends on ARCH_TEGRA
@@ -1476,6 +1498,10 @@ config DEBUG_STI_UART
        bool
        depends on ARCH_STI
 
+config DEBUG_STM32_UART
+       bool
+       depends on ARCH_STM32
+
 config DEBUG_SIRFSOC_UART
        bool
        depends on ARCH_SIRF
@@ -1525,6 +1551,7 @@ config DEBUG_LL_INCLUDE
        default "debug/s5pv210.S" if DEBUG_S5PV210_UART
        default "debug/sirf.S" if DEBUG_SIRFSOC_UART
        default "debug/sti.S" if DEBUG_STI_UART
+       default "debug/stm32.S" if DEBUG_STM32_UART
        default "debug/tegra.S" if DEBUG_TEGRA_UART
        default "debug/ux500.S" if DEBUG_UX500_UART
        default "debug/vexpress.S" if DEBUG_VEXPRESS_UART0_DETECT

diff --git a/arch/arm/include/debug/stm32.S b/arch/arm/include/debug/stm32.S
new file mode 100644 (file)
index 0000000..1abb32f
--- /dev/null
+++ b/arch/arm/include/debug/stm32.S
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) STMicroelectronics SA 2017 - All Rights Reserved
+ * Author:   Gerald Baeza <gerald.baeza@st.com> for STMicroelectronics.
+ */
+
+#define STM32_UART_BASE                        0x40011000      /* USART1 */
+
+#ifdef CONFIG_STM32F4_DEBUG_UART
+#define STM32_USART_SR_OFF             0x00
+#define STM32_USART_TDR_OFF            0x04
+#endif
+
+#ifdef CONFIG_STM32F7_DEBUG_UART
+#define STM32_USART_SR_OFF             0x1C
+#define STM32_USART_TDR_OFF            0x28
+#endif
+
+#define STM32_USART_TC                 (1 << 6)        /* Tx complete       */
+#define STM32_USART_TXE                        (1 << 7)        /* Tx data reg empty */
+
+.macro addruart, rp, rv, tmp
+       ldr     \rp,      =STM32_UART_BASE      @ physical base
+       ldr     \rv,      =STM32_UART_BASE      @ virt base /* NoMMU */
+.endm
+
+.macro  senduart,rd,rx
+       strb    \rd, [\rx, #STM32_USART_TDR_OFF]
+.endm
+
+.macro  waituart,rd,rx
+1001:  ldr     \rd, [\rx, #(STM32_USART_SR_OFF)]       @ Read Status Register
+       tst     \rd, #STM32_USART_TXE                   @ TXE = 1 = tx empty
+       beq     1001b
+.endm
+
+.macro  busyuart,rd,rx
+1001:  ldr     \rd, [\rx, #(STM32_USART_SR_OFF)]       @ Read Status Register
+       tst     \rd, #STM32_USART_TC                    @ TC = 1 = tx complete
+       beq     1001b
+.endm