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Date: Mon, 04 May 2015 18:31:44 -0400
From: Peter Hurley <peter@...leysoftware.com>
To: Robert Schwebel <r.schwebel@...gutronix.de>
CC: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel@...gutronix.de
Subject: Re: earlycon: no match?
On 05/04/2015 05:58 PM, Robert Schwebel wrote:
> On Mon, May 04, 2015 at 05:27:35PM -0400, Peter Hurley wrote:
>> As I understand you,
>>
>> 1. you have CONFIG_SERIAL_EARLYCON=y
>> 2. but you don't specify an earlycon
>> 3. so no earlycon starts.
>> 4. your command line includes "console=ttyAMA0,115200n8"
>> 5. and a console starts on that port (yes?)
>>
>> I don't see a regression here from any previous kernel; this is exactly
>> the same behavior as before, so what is broken?
>
> It outputs a warning message "no match" because it assumes that
> "ttyAMA0" (specified in the console= entry on the kernel commandline)
> matches with "pl011", coming from OF_EARLYCON_DECLARE for the serial
> driver.
>
> I don't understand how this is supposed to work: it will *never* match,
> right?
>
> You say it is a diagnostics message that indicates a misspelling.
> I fail to see what is misspelled, so what does it diagnose?
Ok, so this is only about the diagnostic message, and not about some
other failure.
I don't typically describe harmless diagnostics that didn't appear before
as "broken", so I was having trouble believing what I was reading.
Now that I understand that this is _only_ about a diagnostic message that
didn't appear in previous kernels, I will direct to what I have written
previously multiple times.
Further, I would ask how _you_ would programmatically distinguish
misspellings amongst the following console strings?
console=pl012,...
console=_pl011,...
console=pl,...
console=ttyAMA0,...
Regards,
Peter Hurley
>>> In order to let you better understand the setup here: My AM335x device
>>> (same CPU as on BeagleBone) is a headless embedded system, the only
>>> input/output device it has is a serial port. No display, no touch. For
>>> development, a pretty similar system is simulated in QEMU, with
>>> vexpress.
>>>
>>> Until recently, specifying "console=ttyAMA0" was the correct way to get
>>> the kernel + userspace output out of that serial line. On ARM, there was
>>> no "early" mechanism, only early_printk.
>>>
>>> I wouldn't mind if your citation from kernel-parameters above was true
>>> and I could get an (early and non-early) serial console with a unified
>>> "console=ttyAMA0".
>>>
>>> However, it doesn't work, as "ttyAMA0" doesn't match "pl011".
>>
>> The AM335x does not have a AMBA pl011 port, so "console=ttyAMA0,..." has no
>> effect on that hardware, and never has. Something else is providing console
>> on that setup. Please attach your entire dmesg log for that setup.
>
> Hardware 1: AM335x
> drivers/serial/tty/omap-serial.c
> console=ttyO2,115200n8
>
> Hardware 2: QEMU/vexpress
> drivers/serial/tty/amba-pl011.c
> console=ttyAMA0,38400
>
> The same kernel runs on both platforms.
>
> Let's just discuss the 2nd case for now, with ttyAMA0 (which is pl011),
> which has earlycon support and registers here:
>
> http://lxr.free-electrons.com/source/drivers/tty/serial/amba-pl011.c#L2129
>
>>> So I'm doing the right thing here, and it doesn't work.
>>
>> I'm not sure what you mean by "it doesn't work".
>> Are you saying that the serial console is not starting?
>
> The serial console is starting.
>
> It claims that earlycon has "no match", while the correct serial device
> is specified.
>
> How do you suggest this is supposed to be used in the pl011 case,
> without the "diagnostic message" triggering that says "no match"?
>
> Here is the full serial console log (directed to qemu's stdout):
>
> ----------8<----------8<----------8<----------8<----------8<----------
> rsc@...listo:OSELAS.BSP-GF$ configs/platform-gf/run
> [ 0.000000] Linux version 4.1.0-rc1+ (rsc@...listo) (gcc version 4.8.3 20131111 (prerelease) (OSELAS.Toolchain-2013.12.2 linaro-4.8-2013.11) ) #10 PREEMPT Mon May 4 23:03:27 CEST 2015
> [ 0.000000] earlycon: no match for ttyAMA0,38400n8
> [ 0.000000] Kernel command line: root=/dev/mmcblk0p2 rootfs=ext2 rw mem=1024M console=ttyAMA0,38400n8 loglevel=6 rootwait rootfstype=ext4
PS - If the message really bothers you that much, please feel free to submit a
patch to Greg that lowers that message level to pr_info() instead, so it
doesn't appear in your logs.
I've include an _unsigned_ patch below which does just that. Feel free to
modify and submit it to Greg with your Signed-off-by.
> [ 0.000000] Virtual kernel memory layout:
> [ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
> [ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
> [ 0.000000] vmalloc : 0xf0000000 - 0xff000000 ( 240 MB)
> [ 0.000000] lowmem : 0xc0000000 - 0xef800000 ( 760 MB)
> [ 0.000000] pkmap : 0xbfe00000 - 0xc0000000 ( 2 MB)
> [ 0.000000] modules : 0xbf000000 - 0xbfe00000 ( 14 MB)
> [ 0.000000] .text : 0xc0008000 - 0xc0674ed4 (6580 kB)
> [ 0.000000] .init : 0xc0675000 - 0xc06b2000 ( 244 kB)
> [ 0.000000] .data : 0xc06b2000 - 0xc06fd3e8 ( 301 kB)
> [ 0.000000] .bss : 0xc0700000 - 0xc073a5d8 ( 234 kB)
> [ 0.000000] L2C: platform modifies aux control register: 0x02020000 -> 0x02420000
> [ 0.000000] L2C: DT/platform modifies aux control register: 0x02020000 -> 0x02420000
> [ 0.425170] platform 10000000.sysreg: Error -2 creating of_node link
> [ 0.429607] platform basic-mmio-gpio.1.auto: Error -2 creating of_node link
> [ 0.429959] platform basic-mmio-gpio.2.auto: Error -2 creating of_node link
> [ 0.430561] platform basic-mmio-gpio.3.auto: Error -2 creating of_node link
> [ 0.604531] of_amba_device_create(): amba_device_add() failed (-19) for /memory-controller@...e0000
> [ 0.605709] of_amba_device_create(): amba_device_add() failed (-19) for /memory-controller@...e1000
> [ 0.606411] of_amba_device_create(): amba_device_add() failed (-19) for /watchdog@...e5000
> [ 0.620892] of_amba_device_create(): amba_device_add() failed (-19) for /smb/motherboard/iofpga@7,00000000/sysctl@...00
> [ 0.633512] of_amba_device_create(): amba_device_add() failed (-19) for /smb/motherboard/iofpga@7,00000000/wdt@...00
> [ 0.725997] SCSI subsystem initialized
> [ 0.796591] NFS: Registering the id_resolver key type
> [ 0.797533] Key type id_resolver registered
> [ 0.797758] Key type id_legacy registered
> [ 0.998780] Key type dns_resolver registered
> [ 1.403497] random: nonblocking pool is initialized
>
> Welcome to PTXdist / af inventions-GF!
>
> [ OK ] Created slice Root Slice.
> [ OK ] Listening on Journal Socket (/dev/log).
> [ OK ] Listening on udev Kernel Socket.
>
> <...>
>
> ----------8<----------8<----------8<----------8<----------8<----------
>
> rsc
>
--- >% ---
Subject: [PATCH] earlycon: Reduce log message level of "earlycon: no match for
..."
---
drivers/tty/serial/earlycon.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
index 5fdc9f3..a7725f6 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -188,7 +188,7 @@ static int __init param_setup_earlycon(char *buf)
err = setup_earlycon(buf);
if (err == -ENOENT) {
- pr_warn("no match for %s\n", buf);
+ pr_info("no match for %s\n", buf);
err = 0;
} else if (err == -EALREADY) {
pr_warn("already registered\n");
--
2.4.0
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