Supporting early console on a SERIAL_8250_RT288X platform
Mason
slash.tmp at free.fr
Fri Apr 7 07:53:54 EDT 2017
Hello,
Some drivers hang or panic before the normal console is available.
In these situations, "earlyprintk" is a life-saver.
My problem with earlyprintk is that the UART address needs to be
hard-coded in the kernel binary, which means I can't use the same
binary for two chips with different UART addresses, right?
As far as I understand, "earlycon" helps in that situation, because
it looks up the UART address at run-time in the device tree.
QUESTION #1
Is that the only difference between earlyprintk and earlycon?
(Probably not, see below)
I hacked kernel v4.9.20 to add early console support on my platform.
The patch is provided below, I'd like to hear comments on what needs
fixing... because something is not right. If I call panic() in one of
my driver's probe function, I don't see the output of the panic()
call, which makes the whole exercise rather pointless.
This is what I see:
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 4.9.20-1-rc3 (gcc version 5.3.1 20160113 (Linaro GCC 5.3-2016.02) ) #4 SMP PREEMPT Fri Apr 7 12:57
[ 0.000000] CPU: ARMv7 Processor [413fc090] revision 0 (ARMv7), cr=10c5387d
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt:Machine model: Sigma Designs SMP8758 Vantage-1172 Rev E1
[ 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=palmchip compatible=ralink,rt2880-uart setup=early_palmchip_setup
[ 0.000000] ENTER of_setup_earlycon
[ 0.000000] earlycon: palmchip0 at MMIO 0x00010700 (options '115200n8')
[ 0.000000] bootconsole [palmchip0] enabled
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] percpu: Embedded 14 pages/cpu @cfdd6000 s24704 r8192 d24448 u57344
[ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 65024
[ 0.000000] Kernel command line: mem=256M earlycon
[ 0.000000] PID hash table entries: 1024 (order: 0, 4096 bytes)
[ 0.000000] Dentry cache hash table entries: 32768 (order: 5, 131072 bytes)
[ 0.000000] Inode-cache hash table entries: 16384 (order: 4, 65536 bytes)
[ 0.000000] Memory: 248064K/262144K available (4096K kernel code, 147K rwdata, 892K rodata, 6144K init, 233K bss, 14080K reserved, 0K cma-reserved, 0K highmem)
[ 0.000000] Virtual kernel memory layout:
[ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
[ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
[ 0.000000] vmalloc : 0xd0800000 - 0xff800000 ( 752 MB)
[ 0.000000] lowmem : 0xc0000000 - 0xd0000000 ( 256 MB)
[ 0.000000] pkmap : 0xbfe00000 - 0xc0000000 ( 2 MB)
[ 0.000000] modules : 0xbf000000 - 0xbfe00000 ( 14 MB)
[ 0.000000] .text : 0xc0008000 - 0xc0500000 (5088 kB)
[ 0.000000] .init : 0xc0600000 - 0xc0c00000 (6144 kB)
[ 0.000000] .data : 0xc0c00000 - 0xc0c24c60 ( 148 kB)
[ 0.000000] .bss : 0xc0c24c60 - 0xc0c5f140 ( 234 kB)
[ 0.000000] Preemptible hierarchical RCU implementation.
[ 0.000000] Build-time adjustment of leaf fanout to 32.
[ 0.000000] RCU restricting CPUs from NR_CPUS=4 to nr_cpu_ids=2.
[ 0.000000] RCU: Adjusting geometry for rcu_fanout_leaf=32, nr_cpu_ids=2
[ 0.000000] NR_IRQS:16 nr_irqs:16 16
[ 0.000000] L2C-310 enabling early BRESP for Cortex-A9
[ 0.000000] L2C-310 ID prefetch enabled, offset 4 lines
[ 0.000000] L2C-310 dynamic clock gating enabled, standby mode enabled
[ 0.000000] L2C-310 cache controller enabled, 8 ways, 512 kB
[ 0.000000] L2C-310: CACHE_ID 0x410000c8, AUX_CTRL 0x72860401
[ 0.000000] clocksource: tango-xtal: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 70787423951 ns
[ 0.000003] sched_clock: 32 bits at 27MHz, resolution 37ns, wraps every 79536431085ns
[ 0.007873] Switching to timer-based delay loop, resolution 37ns
[ 0.014146] Console: colour dummy device 80x30
[ 0.018616] console [tty0] enabled
[ 0.022039] bootconsole [palmchip0] disabled
And it just hangs there...
If I remove the panic() call, it boots normally, like this:
...
[ 0.014147] Console: colour dummy device 80x30
[ 0.018616] console [tty0] enabled
[ 0.022039] bootconsole [palmchip0] disabled
[ 0.026345] Calibrating delay loop (skipped), value calculated using timer frequency.. 54.25 BogoMIPS (lpj=90000)
[ 0.026364] pid_max: default: 32768 minimum: 301
...
Did I implement something wrong?
Why am I not seeing the output of the panic() call, like I do
with earlyprintk?
Since tty0 is enabled, why isn't it picking up where palmchip0
left off?
Earlier discussion:
https://www.spinics.net/lists/linux-serial/msg16227.html
This is the patch I'm using:
diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index 85a12f032402..2adabe788c17 100644
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -172,3 +172,52 @@ static int __init early_omap8250_setup(struct earlycon_device *device,
OF_EARLYCON_DECLARE(omap8250, "ti,omap4-uart", early_omap8250_setup);
#endif
+
+#ifdef CONFIG_SERIAL_8250_RT288X
+
+extern unsigned int au_serial_in(struct uart_port *p, int offset);
+extern void au_serial_out(struct uart_port *p, int offset, int value);
+
+/*** Copy serial_putc with s/serial8250_early/au_serial/g ***/
+
+static void __init palmchip_putc(struct uart_port *port, int c)
+{
+ unsigned int status;
+
+ au_serial_out(port, UART_TX, c);
+
+ for (;;) {
+ status = au_serial_in(port, UART_LSR);
+ if ((status & BOTH_EMPTY) == BOTH_EMPTY)
+ break;
+ cpu_relax();
+ }
+}
+
+/*** Copy early_serial8250_write with s/serial_putc/palmchip_putc/g ***/
+
+static void __init early_palmchip_write(struct console *console,
+ const char *s, unsigned int count)
+{
+ struct earlycon_device *device = console->data;
+ struct uart_port *port = &device->port;
+
+ //extern void printascii(const char *); printascii("EARLY: ");
+ uart_console_write(port, s, count, palmchip_putc);
+}
+
+static int __init early_palmchip_setup(struct earlycon_device *device,
+ const char *options)
+{
+ struct uart_port *port = &device->port;
+
+ if (!(device->port.membase || device->port.iobase))
+ return -ENODEV;
+
+ port->regshift = 2; /* Hard coding the value doesn't feel right */
+ device->con->write = early_palmchip_write;
+ return 0;
+}
+OF_EARLYCON_DECLARE(palmchip, "ralink,rt2880-uart", early_palmchip_setup);
+
+#endif
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 080d5a59d0a7..7eb60146cb3f 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -313,7 +313,7 @@ static void default_serial_dl_write(struct uart_8250_port *up, int value)
-1, /* UART_SCR (unmapped) */
};
-static unsigned int au_serial_in(struct uart_port *p, int offset)
+/*static*/ unsigned int au_serial_in(struct uart_port *p, int offset)
{
if (offset >= ARRAY_SIZE(au_io_in_map))
return UINT_MAX;
@@ -323,7 +323,7 @@ static unsigned int au_serial_in(struct uart_port *p, int offset)
return __raw_readl(p->membase + (offset << p->regshift));
}
-static void au_serial_out(struct uart_port *p, int offset, int value)
+/*static*/ void au_serial_out(struct uart_port *p, int offset, int value)
{
if (offset >= ARRAY_SIZE(au_io_out_map))
return;
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