drivers: imx: crash-console: Add a mxc_crash_console driver

This patch does two main things

- It implements the crash console UART init in assembly, as a
  hard-coded 115200 8N1 assumed from the 24 MHz clock.

  If the clock setup code has not run yet, this code can't work but,
  setting up clocks and clock-gates is way out of scope for this type of
  recovery function.

- It adds code to write a character out of the NXP UART without using any
  stack-based operations when doing so.

- Provides support for crash console in DCE or DTE mode.

Signed-off-by: Bryan O'Donoghue <[email protected]>

diff --git a/drivers/imx/uart/imx_crash_uart.S b/drivers/imx/uart/imx_crash_uart.S
new file mode 100644 (file)
index 0000000..aa987b3
--- /dev/null
+++ b/drivers/imx/uart/imx_crash_uart.S
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) Linaro 2018 Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#include <arch.h>
+#include <asm_macros.S>
+#include <assert_macros.S>
+#include <imx_uart.h>
+#include <platform_def.h>
+
+       .globl  imx_crash_uart_init
+       .globl  imx_crash_uart_putc
+
+       /* -----------------------------------------------
+        * int imx_crash_uart_init(uintptr_t base_addr,
+        * unsigned int uart_clk, unsigned int baud_rate)
+        * Function to initialize the console without a
+        * C Runtime to print debug information. This
+        * function will be accessed by console_init and
+        * crash reporting.
+        * In: r0 - console base address
+        *     r1 - Uart clock in Hz
+        *     r2 - Baud rate
+        * Out: return 1 on success else 0 on error
+        * Clobber list : r1, r2, r3, r4
+        * -----------------------------------------------
+        */
+func imx_crash_uart_init
+       /* Free up r1 as a scratch reg */
+       mov     r4, r0
+       mov     r0, r1
+
+       /* Reset UART via CR2 */
+       add     r1, r4, #IMX_UART_CR2_OFFSET
+       movs    r3, #0
+       str     r3, [r4, #IMX_UART_CR2_OFFSET]
+
+       /* Wait for reset complete */
+__wait_cr2_reset:
+       ldr     r3, [r1, #0]
+       ands    r3, #IMX_UART_CR2_SRST
+       beq     __wait_cr2_reset
+
+       /* Enable UART */
+       movs    r3, #IMX_UART_CR1_UARTEN
+       mov     r1, r2
+       str     r3, [r4, #IMX_UART_CR1_OFFSET]
+
+       /*
+        * Ignore RTC/CTS - disable reset
+        * Magic value #16423 =>
+        * IMX_UART_CR2_IRTS | IMX_UART_CR2_WS | IMX_UART_CR2_TXEN | IMX_UART_CR2_RXEN | IMX_UART_CR2_SRST
+        */
+       movw    r3, #16423
+       str     r3, [r4, #IMX_UART_CR2_OFFSET]
+
+       /*
+        * No parity, autobaud detect-old, rxdmuxsel=1 (fixed i.mx7)
+        * Magic value => #132
+        * IMX_UART_CR3_ADNIMP | IMX_UART_CR3_RXDMUXSEL
+        */
+       movs    r3, #132
+       str     r3, [r4, #IMX_UART_CR3_OFFSET]
+
+       /*
+        * Set CTS FIFO trigger to 32 bytes bits 15:10
+        * Magic value => #32768
+        * FIFO trigger bitmask 100000
+        * */
+       mov     r3, #32768
+       str     r3, [r4, #IMX_UART_CR4_OFFSET]
+
+       /*
+        * TX/RX-thresh = 2 bytes, DCE (bit6 = 0), refclk @24MHz / 4
+        * Magic value #2562
+        * IMX_UART_FCR_TXTL(TX_RX_THRESH) | IMX_UART_FCR_RXTL(TX_RX_THRESH) | IMX_UART_FCR_RFDIV2
+        */
+       #ifdef IMX_UART_DTE
+       movw    r3, #2626
+       #else
+       movw    r3, #2562
+       #endif
+       str     r3, [r4, #IMX_UART_FCR_OFFSET]
+
+       /* This BIR should be set to 0x0F prior to writing the BMR */
+       movs    r3, #15
+       str     r3, [r4, #IMX_UART_BIR_OFFSET]
+
+       /* Hard-code to 115200 @ 24 MHz */
+       movs    r0, #104
+       str     r0, [r4, #IMX_UART_BMR_OFFSET]
+
+       /* Indicate success */
+       movs    r0, #1
+       bx      lr
+endfunc imx_crash_uart_init
+
+       /* --------------------------------------------------------
+        * int imx_crash_uart_putc(int c, uintptr_t base_addr)
+        * Function to output a character over the console. It
+        * returns the character printed on success or -1 on error.
+        * In : r0 - character to be printed
+        *      r1 - console base address
+        * Out : return -1 on error else return character.
+        * Clobber list : r2
+        * --------------------------------------------------------
+        */
+func imx_crash_uart_putc
+       /* Output specified character to UART shift-register */
+       str     r0, [r1, #IMX_UART_TXD_OFFSET]
+
+        /* Wait for transmit IMX_UART_STAT2_OFFSET.IMX_UART_STAT2_TXDC == 1 */
+__putc_spin_ready:
+       ldr     r2, [r1, #IMX_UART_STAT2_OFFSET]
+       ands    r2, #IMX_UART_STAT2_TXDC
+       beq     __putc_spin_ready
+
+        /* Transmit complete do we need to fixup \n to \n\r */
+       cmp     r0, #10
+       beq     __putc_fixup_lf
+
+       /* No fixup necessary - exit here */
+       movs    r0, #0
+       bx      lr
+
+       /* Fixup \n to \n\r */
+__putc_fixup_lf:
+       movs    r0, #13
+       b       imx_crash_uart_putc
+endfunc imx_crash_uart_putc