On 05/04/2015 03:42 PM, Robert Schwebel wrote:
> Hi Peter,
>
> On Mon, May 04, 2015 at 10:01:37AM -0400, Peter Hurley wrote:
>>> with 4.1-rc1, my boxes with early console enabled show something like
>>> this (the example is vexpress, but it for example also happens on an
>>> AM335x board):
>>>
>>> earlycon: no match for ttyAMA0,38400n8
>>
>> This shouldn't impact any previous earlycon setup. Are you saying
>> you're seeing a regression?
>
> Well, it is a warning, and the system was warning-free on mainline with
> the last kernels. People assume something is wrong if they read such a
> message, so I'm searching for a way to do it right and get rid of the
> warning again.
It's not a warning; it's simply a diagnostic in case the earlycon was
misspelled. Since 2007, 'console=' is a early param synonym for 'earlycon=';
IOW, the message is new but not the behavior.
>> How do you have early console enabled, via the command line or via DT?
>
> Neither nor: the same SD card image runs on qemu (vexpress) and on an
> AM335x. It has its primary console on the serial console:
>
> - console=ttyAMA0,38400 (amba-pl011.c, vexpress)
> - console=ttyO2,115200n8 (omap-serial.c, AM335x)
>
> There is no "earlycon" on the commandline and nothing earlycon related I
> did on purpose in the oftree.
Ok. In your first email, you said "my boxes with early console enabled",
so I thought you meant that you were starting an earlycon. I see now
you meant enabled, as in built-in (not enabled as in started).
> My expectation would be to configure the system in a way that I have
> everything necessary for earlecon usage compiled into the kernel, so I
> can enable it manually from the bootloader whenever I need it (i.e. by
> adding 'earlycon' to the kernel commandline, or by modifying the oftree
> before it is handled over to the kernel).
Ok.
>>> The box was booted with "console=ttyAMA0,38400n8" on the commandline.
>>> If I understand this right, the code in drivers/tty/serial/earlycon.c
>>> calls setup_earlycon() with the string above ("ttyAMA0,38400n8") and
>>> fails to find that string in the "names" part of the __earlycon_table,
>>> because for the pl011 component on vexpress, the early console was
>>> registered in drivers/tty/serial/amba-pl011.c with:
>>>
>>> OF_EARLYCON_DECLARE(pl011, "arm,pl011", pl011_early_console_setup);
>>> ^^^^^ name
>>>
>>> So isn't that trying to match "ttyAMA0" against "arm,pl011"? I have the
>>> feeling that I didn't understand the logic behind that.
>>>
>>> Can you elaborate about how this is supposed to work correctly?
The facility I describe below is to enable earlycon->console handoff.
If you're not interested in that, please disregard.
I provided the description because it wasn't clear to me from your
original email if that was something you were trying to implement and
couldn't get working.
>> Yeah, I've been meaning to write about this but simply haven't had the
>> time yet; apologies for that.
>>
>> The facility is hopefully best explained by the existing 8250 exemplar.
>> Normally, an 8250 early console is started via command line with a
>> command line parameter like:
>>
>> earlycon=uart,io,0x2f8,115200n8
>
> What happens if you don't have this parameter on the kernel commandline,
> but use the same port for your serial console? i.e. 'console=ttyS0'?
>
> I would expect the same warning I see on my boxes.
The diagnostic was added in commit 470ca0de69feaba5df215ad804cec1859883a5ed
("serial: earlycon: Enable earlycon without command line param").
Previously, if earlycon failed to start because of an error, such as because the
earlycon name was misspelled, there was no diagnostic.
>> Since 2007, an 8250 early console can also be started via command line
>> using console= instead, like:
>>
>> console=uart,io,0x2f8,115200n8
>
> No: "console=..." puts the console on that port, not the early console.
> The semantic for console= was always to specify the name of the device
> there, so "console=ttyS0...", not "console=uart...", right?
>From Documentation/kernel-parameters:
console= [KNL] Output console device and options.
....
uart[8250],io,<addr>[,options]
uart[8250],mmio,<addr>[,options]
uart[8250],mmio32,<addr>[,options]
uart[8250],0x<addr>[,options]
Start an early, polled-mode console on the 8250/16550
UART at the specified I/O port or MMIO address,
switching to the matching ttyS device later.
MMIO inter-register address stride is either 8-bit
(mmio) or 32-bit (mmio32).
If none of [io|mmio|mmio32], <addr> is assumed to be
equivalent to 'mmio'. 'options' are specified in the
same format described for ttyS above; if unspecified,
the h/w is not re-initialized.
This behavior was added in Jul 2007 with commit 18a8bd949d6adb311
("serial: convert early_uart to earlycon for 8250").
>> In this alternate form, this early console will go on to become the
>> corresponding ttyS console.
>>
>> However, that functionality was exclusive to 8250 console/earlycon.
>> To get this same behavior for the amba-pl011 console would look
>> something like:
>>
>> /* drivers/tty/serial/amba-pl011.c */
>>
>> /* returns 0 if the console matches; otherwise, non-zero to use default matching */
>> static int pl011_console_match(struct console *co, char *name, int idx, char *options)
>> {
>> unsigned char iotype;
>> unsigned long addr;
>>
>> if (strncmp(name, "pl" 2) != 0 || idx != 11)
>> return -ENODEV;
>>
>> if (uart_parse_earlycon(options, &iotype, &addr, &options))
>> return -ENODEV;
>>
>> /* find the port from the addr */
>> for (i = 0; i < ARRAY_SIZE(amba_ports); i++) {
>> if (amba_ports[i] == NULL)
>> continue;
>> if (port->mapbase != addr)
>> continue;
>>
>> co->index = i;
>> return pl011_console_setup(co, options);
>> }
>>
>> return -ENODEV;
>> }
>>
>> ...
>>
>> static struct console amba_console = {
>> ...
>> .match = pl011_console_match,
>> ...
>> };
>
> pl011 already has:
>
> ----------8<----------8<----------8<----------8<----------8<----------8<----------
>
> static void pl011_early_write(struct console *con, const char *s, unsigned n)
> {
> struct earlycon_device *dev = con->data;
>
> uart_console_write(&dev->port, s, n, pl011_putc);
> }
>
> static int __init pl011_early_console_setup(struct earlycon_device *device,
> const char *opt)
> {
> if (!device->port.membase)
> return -ENODEV;
>
> device->con->write = pl011_early_write;
> return 0;
> }
> EARLYCON_DECLARE(pl011, pl011_early_console_setup);
> OF_EARLYCON_DECLARE(pl011, "arm,pl011", pl011_early_console_setup);
>
> ----------8<----------8<----------8<----------8<----------8<----------8<----------
>
> So on oftree based systems it registers an __earlycon_table with name=pl011 and
> compatible=arm,pl011. In order to see something, I need to add
>
> console=ttyAMA0
>
> In that case, it doesn't matter if I add an earlycon= parameter on the
> commandline or not. The system takes the console= entry and hands it over to
> setup_earlycon(), which tries to match it against the __earlycon_table, where
> it doesn't find anything. Simply because it is pl011 there.
>
> So switching earlycon on is broken.
>
> If I leave out earlycon, I'd expect to switch off earlycon, which doesn't work,
> because exactly the same as above happens.
>
> So switching earlycon off is also broken.
>
> This is either buggy or I didn't understand how it is supposed to be used.
AFAICT nothing is broken; you're only seeing a new diagnostic from code that
was always running.
Regards,
Peter Hurley
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