Re: [PATCH V3 09/10] tty: serial: of-serial: Allow OF earlycon to default to "on"

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Wed, Oct 22, 2014 at 9:47 PM, Rob Herring <robh@xxxxxxxxxx> wrote:
>> Now that earlycon can get all of its parameters from DT, do you think
>> it might make sense to drop the command line option entirely from
>> fdt.c and enable it all of the time if stdout-path is set correctly?
>>
>> From the user's standpoint, how important is it to be able to run
>> without earlycon?
>
> It may affect boot time for one although if you care you probably
> disable console altogether.
>
> I think we'd just have to add a noearlycon option instead if we made
> it the default. It's never been the default before, so I don't think
> we should change now. There's also an implicit requirement that the
> bootloader has configured the uart already. You could easily hang if
> the uart has not been setup.

EARLY_PRINTK is enabled by default on MIPS platforms that support it.
I have been using this for years and found it very helpful in
debugging failures in the kernel boot process (especially intermittent
ones).

But for a new platform it is better to use earlycon as earlycon
provides a clean way of reading the UART information out of DT.  My
original bcm3384 (MIPS) port used EARLY_PRINTK but I recently
converted it to earlycon.  The last remaining goal is to get it
enabled by default again.

>> Would it be more straightforward to have the arch code explicitly call
>> early_init_dt_scan_chosen_serial() to indicate that it is ready for
>> the early UART driver to run?
>
> Yes, but then when do you handle earlycon command line option for
> non-DT case? Having these at different points in time is asking for
> problems.

Is it important for the non-DT "earlycon" option to be handled from
parse_early_param() just because parse_early_param() runs at the right
point in the boot sequence (not because we actually wanted it to be a
command line option)?

One other option might be to invoke early_init_dt_scan_chosen_serial()
from parse_early_param().  But it is somewhat clunky to put a special
case in there...
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux PPP]     [Linux FS]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Linmodem]     [Device Mapper]     [Linux Kernel for ARM]

  Powered by Linux