On 03/03/2017 18:46, Russell King - ARM Linux wrote:
> On Fri, Mar 03, 2017 at 06:26:28PM +0100, Andreas Färber wrote:
>
>> Am 03.03.2017 um 17:55 schrieb Russell King - ARM Linux:
>>
>>> On Fri, Mar 03, 2017 at 05:42:02PM +0100, Marc Gonzalez wrote:
>>>
>>>> I'm confused about early consoles and earlyprintk, and all that good stuff.
>>>> When my kernel panics, I don't get the expected output.
>>>>
>>>> Using "mem=256M ignore_loglevel earlyprintk"
>>>>
>>>> [ 0.014325] Console: colour dummy device 80x30
>>>> [ 0.018885] console [tty0] enabled
>>>> [ 0.022396] bootconsole [earlycon0] disabled
>>>>
>>>> And it hangs there.
>>>
>>> tty0 is the kernel virtual terminal console, which is what appears on
>>> VGA or framebuffers. This is the default console if nothing else is
>>> specified.
>>>
>>> What happened here is that the virtual terminal console registered, was
>>> detected to be the system console, so early console was shut down, and
>>> the boot messages logged to the virtual terminal console instead.
>>
>> Why does passing console= make a difference though?
>>
>> I expect stdout-path to have the same effect as the command line, and I
>> am pretty sure that that was previous behavior in, e.g., v4.4.
>>
>> Note that I am using earlycon, as opposed to earlyprintk above.
>
> The property is:
>
> stdout-path = "dt-node-name:hw-parameters";
>
> and this is parsed by the code in drivers/of/fdt.c,
> early_init_dt_scan_chosen_stdout() (briefly):
>
> offset = fdt_path_offset(fdt, "/chosen");
> p = fdt_getprop(fdt, offset, "stdout-path", &l);
>
> q = strchrnul(p, ':');
> if (*q != '\0')
> options = q + 1;
> l = q - p;
>
> /* Get the node specified by stdout-path */
> offset = fdt_path_offset_namelen(fdt, p, l);
> if (offset < 0) {
> pr_warn("earlycon: stdout-path %.*s not found\n", l, p);
>
> So here, offset points at the node named by "dt-node-name" above.
>
> This function then tries to patch the specified node's compatible with
> the drivers in the __earlycon_table:
>
> for (match = __earlycon_table; match < __earlycon_table_end; match++) {
> if (!match->compatible[0])
> continue;
>
> if (fdt_node_check_compatible(fdt, offset, match->compatible))
> continue;
>
> and when a match is found, calls:
>
> of_setup_earlycon(match, offset, options);
>
> Here, we go into the code in drivers/tty/serial/earlycon.c, which reads
> the standard properties (like "reg", etc) filling out a uart_port
> before calling the early console's ->setup method. If everything goes
> to plan, register_console() is called to register the early console.
>
> So there's nothing there which changes the default system console.
>
> The next place is of_alias_scan() in drivers/of/base.c. This records
> the device_node and options in of_stdout and of_stdout_options
> respectively - it, again, does not change the default system console.
>
> When a serial console is initialised, of_console_check() gets called by
> serial core to check whether the DT node for it is "of_stdout", and if
> it matches, it modifies the preferred system console.
>
> This all looks good, and one might expect that it has the desired
> effect, but this code is fatally flawed in design: the point at which
> of_console_check() gets called is _way_ after consoles like the virtual
> terminal console get initialised. What this means is that, at the point
> in time that the virtual terminal is initialised, as far as the console
> system is concerned, the preferred console is still the virtual terminal.
> It knows nothing about the desire for a different console.
>
> Given the current console handling, it's not easy to solve without
> overhauling the way consoles are chosen - the root problem is that the
> Linux console system works via Linux device driver names and indexes,
> and there's no easy way to translate a DT stdout-path property to a
> Linux device driver name and index without the driver having been
> initialised.
Time for me to take another stab at this issue.
Relevant parts of my DT:
aliases { serial = &uart; };
chosen { stdout-path = "serial:115200n8"; };
uart: serial@10700 {
compatible = "ralink,rt2880-uart";
reg = <0x10700 0x30>;
interrupts = <1 IRQ_TYPE_LEVEL_HIGH>;
clock-frequency = <7372800>;
reg-shift = <2>;
};
Relevant part of my kernel config:
CONFIG_FIX_EARLYCON_MEM=y
CONFIG_GENERIC_EARLY_IOREMAP=y
CONFIG_OF_EARLY_FLATTREE=y
#
# Character devices
#
CONFIG_TTY=y
CONFIG_VT=y
CONFIG_CONSOLE_TRANSLATIONS=y
CONFIG_VT_CONSOLE=y
CONFIG_HW_CONSOLE=y
# CONFIG_VT_HW_CONSOLE_BINDING is not set
CONFIG_UNIX98_PTYS=y
CONFIG_LEGACY_PTYS=y
CONFIG_LEGACY_PTY_COUNT=256
# CONFIG_SERIAL_NONSTANDARD is not set
#
# Serial drivers
#
CONFIG_SERIAL_EARLYCON=y
CONFIG_SERIAL_8250=y
# CONFIG_SERIAL_8250_DEPRECATED_OPTIONS is not set
# CONFIG_SERIAL_8250_FINTEK is not set
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_SERIAL_8250_DMA=y
CONFIG_SERIAL_8250_PCI=y
CONFIG_SERIAL_8250_NR_UARTS=4
CONFIG_SERIAL_8250_RUNTIME_UARTS=4
# CONFIG_SERIAL_8250_EXTENDED is not set
CONFIG_SERIAL_8250_FSL=y
# CONFIG_SERIAL_8250_DW is not set
# CONFIG_SERIAL_8250_EM is not set
CONFIG_SERIAL_8250_RT288X=y
# CONFIG_SERIAL_8250_MOXA is not set
CONFIG_SERIAL_OF_PLATFORM=y
#
# Non-8250 serial port support
#
# CONFIG_SERIAL_EARLYCON_ARM_SEMIHOST is not set
# CONFIG_SERIAL_UARTLITE is not set
CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y
# CONFIG_SERIAL_JSM is not set
# CONFIG_SERIAL_SCCNXP is not set
# CONFIG_SERIAL_SC16IS7XX is not set
# CONFIG_SERIAL_BCM63XX is not set
# CONFIG_SERIAL_ALTERA_JTAGUART is not set
# CONFIG_SERIAL_ALTERA_UART is not set
# CONFIG_SERIAL_XILINX_PS_UART is not set
# CONFIG_SERIAL_ARC is not set
# CONFIG_SERIAL_RP2 is not set
# CONFIG_SERIAL_FSL_LPUART is not set
# CONFIG_SERIAL_CONEXANT_DIGICOLOR is not set
# CONFIG_SERIAL_ST_ASC is not set
# CONFIG_SERIAL_STM32 is not set
# CONFIG_HVC_DCC is not set
# CONFIG_IPMI_HANDLER is not set
# CONFIG_HW_RANDOM is not set
# CONFIG_R3964 is not set
# CONFIG_APPLICOM is not set
# CONFIG_RAW_DRIVER is not set
# CONFIG_TCG_TPM is not set
CONFIG_DEVPORT=y
# CONFIG_XILLYBUS is not set
CONFIG_DEBUG_LL_INCLUDE="mach/debug-macro.S"
# CONFIG_DEBUG_UART_8250 is not set
CONFIG_UNCOMPRESS_INCLUDE="debug/uncompress.h"
Booting with mem=256M console=ttyS0,115200
[ 0.000213] Console: colour dummy device 80x30
[ 0.418383] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 0.419837] console [ttyS0] disabled
[ 0.419983] 10700.serial: ttyS0 at MMIO 0x10700 (irq = 20, base_baud = 460800) is a Palmchip BK-3103
[ 1.000504] console [ttyS0] enabled
Booting with mem=256M
[ 0.000212] Console: colour dummy device 80x30
[ 0.000547] console [tty0] enabled
[ 0.427260] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 0.428970] 10700.serial: ttyS0 at MMIO 0x10700 (irq = 20, base_baud = 460800) is a Palmchip BK-3103
[ 1.007672] console [ttyS0] enabled
Booting with mem=256M earlycon
[ 0.000000] ENTER param_setup_earlycon
[ 0.000000] ENTER early_init_dt_scan_chosen_stdout
[ 0.000000] early_init_dt_scan_chosen_stdout: scan __earlycon_table
[ 0.000000] name=uart compatible=snps,dw-apb-uart setup=early_serial8250_setup
[ 0.000000] name=uart compatible=nvidia,tegra20-uart setup=early_serial8250_setup
[ 0.000000] name=ns16550a compatible=ns16550a setup=early_serial8250_setup
[ 0.000000] name=ns16550 compatible=ns16550 setup=early_serial8250_setup
[ 0.000000] early_init_dt_scan_chosen_stdout: NO MATCH, return ENODEV
[ 0.000000] Malformed early option 'earlycon'
[ 0.000215] Console: colour dummy device 80x30
[ 0.000583] console [tty0] enabled
[ 0.420043] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 0.421945] 10700.serial: ttyS0 at MMIO 0x10700 (irq = 20, base_baud = 460800) is a Palmchip BK-3103
[ 1.014251] console [ttyS0] enabled
drivers/tty/serial/8250/8250_early.c
int __init early_serial8250_setup(struct earlycon_device *device, const char *options)
EARLYCON_DECLARE(uart8250, early_serial8250_setup);
EARLYCON_DECLARE(uart, early_serial8250_setup);
OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
I'm not matching anything, because my UART compatible string is:
uart: serial@10700 {
compatible = "ralink,rt2880-uart";
If I append "ns16550a" or "ns16550", the kernel hangs from the start:
Starting kernel ...
@
But if I add DEBUG_LL support with
CONFIG_DEBUG_LL=y
CONFIG_DEBUG_LL_UART_8250=y
CONFIG_DEBUG_UART_PHYS=0x10700
CONFIG_DEBUG_UART_VIRT=0xf0010700
CONFIG_DEBUG_UART_8250_WORD=y
CONFIG_DEBUG_UART_8250_PALMCHIP=y
and replace the implementation of vprintk_emit() with a very quick and dirty
char buf[400];
extern void printascii(const char *);
text_len = vsnprintf(buf, sizeof buf, fmt, args);
printascii(buf);
return text_len;
then the kernel boots correctly, and I see the following relevant logs:
ENTER param_setup_earlycon
ENTER early_init_dt_scan_chosen_stdout
early_init_dt_scan_chosen_stdout: scan __earlycon_table
name=uart compatible=snps,dw-apb-uart setup=early_serial8250_setup
name=uart compatible=nvidia,tegra20-uart setup=early_serial8250_setup
name=ns16550a compatible=ns16550a setup=early_serial8250_setup
ENTER of_setup_earlycon
earlycon: ns16550a0 at MMIO 0x00010700 (options '115200n8')
bootconsole [ns16550a0] enabled
Kernel command line: mem=256M earlycon
Console: colour dummy device 80x30
console [tty0] enabled
bootconsole [ns16550a0] disabled
Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
10700.serial: ttyS0 at MMIO 0x10700 (irq = 20, base_baud = 460800) is a Palmchip BK-3103
console [ttyS0] enabled
I think the problem is that my UART (Palmchip BK-3103) requires
custom accessors to read/write 16550 registers. And these accessors
are probably ignored this early in the boot.
drivers/tty/serial/8250/8250_port.c
#ifdef CONFIG_SERIAL_8250_RT288X
/* Au1x00/RT288x UART hardware has a weird register layout */
static const s8 au_io_in_map[8] = {
0, /* UART_RX */
2, /* UART_IER */
3, /* UART_IIR */
5, /* UART_LCR */
6, /* UART_MCR */
7, /* UART_LSR */
8, /* UART_MSR */
-1, /* UART_SCR (unmapped) */
};
It is likely that I need to register a specific OF_EARLYCON_DECLARE,
like OMAP did?
Regards.
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