[U-Boot] AM335x configurations - console output at early stages lost

[Vasili Galka]

Hi Simon,

On Mon, May 4, 2015 at 7:45 PM, Simon Glass <sjg at chromium.org> wrote:

> Hi Vasili,
>
> On 4 May 2015 at 10:21, Vasili Galka <vvv444 at gmail.com> wrote:
> >
> > Hi Simon,
> >
> > On Thu, Apr 30, 2015 at 3:38 AM, Simon Glass <sjg at chromium.org> wrote:
> >>
> >> Hi Vasili,
> >>
> >> On 29 April 2015 at 10:57, Vasili Galka <vvv444 at gmail.com> wrote:
> >> > Hi Tom,
> >> >
> >> > I’m working on rebasing an old U-Boot branch for our company’s AM335x
> >> > based board upon the current U-Boot release (v2015.04). Our branch was
> >> > initially based on the v2013.10 release (the ti/am335x/ board was
> >> > taken as reference).
> >> >
> >> > After making all the code compile, I discovered there was a change in
> >> > the U-Boot initialization sequence, introduced by commit
> >> > a6b541b09022acb6f7c2754100ae26bd44eed1d9, that prevents our code from
> >> > working:
> >> >
> >> > Prior to the above mentioned commit, the console serial port was
> >> > initialized at a very early stage in the armv7/am335x/board.c:s_init()
> >> > function (calling preloader_console_init()). Roughly saying, it was
> >> > the first thing done by the SPL code. This made quite much sense, as
> >> > it enabled all the code afterwards to output status/debugging info to
> >> > the console.
> >> > Moving the preloader_console_init() call to spl_board_init() caused it
> >> > to be run at a very "late" stage (as part of the board_init_r()
> >> > function). AFAIU, now all the code that runs till then has no ability
> >> > for any console output.
> >> > For example, in our particular case, the DDR configuration code (in
> >> > sdram_init()) reads the DDR type from an I2C EEPROM. Obviously, if
> >> > something goes wrong in this process, we would like to report it to
> >> > the console.
> >> >
> >> > I understand there was a good reason for the mentioned commit (the
> >> > GD), however, as you see, we have also lost some important
> >> > functionality with it. I would appreciate your advice on how to solve
> >> > it.
> >>
> >> It would certainly be very useful and it would be great if we could
> >> printf() from as soon as we have a stack (and perhaps printch() even
> >> earlier). I think it can be done, but I have not put in the time to
> >> figure it out.
> >>
> >> You could take a look at CONFIG_DEBUG_UART which at least allows
> >> primitive UART access before gd is set up. I wonder if we could do
> >> something like change printf() /purchatr() to use this when gd is
> >> NULL?
> >>
> >> Regards,
> >> Simon
> >
> >
> > Thanks for the suggestion! I'm attempting to make it work.
> > Was the "Debug UART" code (added in
> 21d004368fc8a4da07147c58dfe9a4e16d4ab761) ever tested on AM335x? It does
> not seem to work for me, I'm currently debugging in attempt to understand
> the cause.
>
> From memory I think I did test it locally but did not send patches to
> enable it.
>
> You will need to enable DEBUG_UART_NS16550, and supply suitable values
> for DEBUG_UART_BASE and DEBUG_UART_CLOCK.
>
> But the debug UART code (in ns16550.c) is really simple so it should
> not be possible to debug it.
>
> I think it would be good to have the DEBUG_UART_... options in the
> board's defconfig file, even though CONFIG_DEBUG_UART itself is
> disabled. Then people can enable it easily when they want to use the
> debug UART.
>
> Regards,
> Simon
>

Yes, of course, please see below the changes I applied. I expected to see a
character written on to the UART, but I see nothing. So I attempt to
compare the new serial code to the old one (from 2013) that definitely
works.

Best,
Vasili

---
diff --git a/arch/arm/cpu/armv7/am33xx/board.c
b/arch/arm/cpu/armv7/am33xx/board.c
index 67bef23..79026d4 100644
--- a/arch/arm/cpu/armv7/am33xx/board.c
+++ b/arch/arm/cpu/armv7/am33xx/board.c
@@ -35,6 +35,7 @@
 #include <linux/usb/musb.h>
 #include <asm/omap_musb.h>
 #include <asm/davinci_rtc.h>
+#include <debug_uart.h>

 DECLARE_GLOBAL_DATA_PTR;

@@ -297,6 +298,11 @@ void s_init(void)
     set_uart_mux_conf();
     setup_clocks_for_console();
     uart_soft_reset();
+#ifdef CONFIG_DEBUG_UART
+    debug_uart_init();
+    printch('A');
+    for(;;);
+#endif
 #if defined(CONFIG_NOR_BOOT) || defined(CONFIG_QSPI_BOOT)
     /* TODO: This does not work, gd is not available yet */
     gd->baudrate = CONFIG_BAUDRATE;
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 03beab5..7674433 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -54,7 +54,7 @@ DECLARE_GLOBAL_DATA_PTR;
 #define CONFIG_SYS_NS16550_IER  0x00
 #endif /* CONFIG_SYS_NS16550_IER */

-#ifdef CONFIG_DM_SERIAL
+#if defined(CONFIG_DM_SERIAL) || defined(CONFIG_DEBUG_UART_NS16550)

 static inline void serial_out_shift(unsigned char *addr, int shift, int
value)
 {
@@ -85,6 +85,9 @@ static inline int serial_in_shift(unsigned char *addr,
int shift)
     return readb(addr);
 #endif
 }
+#endif
+
+#if defined(CONFIG_DM_SERIAL)

 static void ns16550_writeb(NS16550_t port, int offset, int value)
 {
diff --git a/include/configs/vm_am335x.h b/include/configs/vm_am335x.h
index 9725c3f..3a1abc9 100644
--- a/include/configs/vm_am335x.h
+++ b/include/configs/vm_am335x.h
@@ -69,6 +69,11 @@
 #define CONFIG_SYS_NS16550_COM1        0x44e09000    /* Baseboard has
UART0 */
 #define CONFIG_BAUDRATE            115200

+/* Enable "debug UART" to be the same (this is used at very beginning
before gd is set-up) */
+#define CONFIG_DEBUG_UART
+#define CONFIG_DEBUG_UART_NS16550
+#define CONFIG_DEBUG_UART_BASE        CONFIG_SYS_NS16550_COM1
+#define CONFIG_DEBUG_UART_CLOCK        CONFIG_SYS_NS16550_CLK

 /*
  * Default to using SPI for environment, etc.