On 08/17/2018 08:57 AM, Petr Mladek wrote:
> On Fri 2018-08-17 07:06:56, Prarit Bhargava wrote:
>> On 08/17/2018 06:50 AM, Sergey Senozhatsky wrote:
>>>> Like I mentioned to Petr, I'd like to know if you (or anyone else) has
>>>> strong
>>>> feelings about changing the behaviour of earlycon on x86? I could make it
>>>> so
>>>> that specifying just earlycon would also initialize the console.
>>>
>>> x86 people and/or scheduler people might have strong opinions on this.
>>> I Cc-ed Peter Zijlstra; he represents both groups and is known to be
>>> a hardcore earlycon user.
>>
>> Thanks, I'm a user of earlycon too, but only moderately.
>>
>> peterz, to give you an overview: Currently on x86, the SPCR information is
>> only
>> interpreted by the early console code, and can be enabled with kernel
>> parameter
>> "earlycon" (no arguments). In this patch I'm proposing adding "console=auto"
>> that would enable the console based on the SPCR data.
>>
>> There are two options on the table. One, we could go with this patch which
>> would make users do "earlycon console=auto" or, I could just change the
>> behaviour of earlycon (no arguments) to also bring up the console. In the
>> second case the kernel parameter would just be "earlycon". There is
>> precedent
>> for the second option as arm64 enables both the earlycon and console by
>> default
>> if SPCR is present. However, on x86, I know many users do not want the
>> console
>> enabled by default so we should keep it on demand.
>>
>> tl;dr: Pick one
>>
>> Option 1: earlycon enables both the early console and console.
>
> I am afraid that this is not acceptable. Users are sensitive
> when a new kernel suddenly enables different consoles. For example,
> see:
>
> + commit dac8bbbae1d0ccba9 ("Revert "printk: fix double printing with
> earlycon")
>
> + commit c6c7d83b9c9e6a8b3 ("Revert "console: don't prefer first
> registered if DT specifies stdout-path")
>
>
> By other words, the new behavior must depend on a new option.
>
>
>> Option 2: earlycon only enables the early console, and console=auto enables
>> the
>> console.
>
> I suggest:
>
> Option 3: "earlycon" enables early console defined by SPCR
> "console" enables console defined by SPCR
>
> I mean that "console" without extra options would enable the console
> defined by ACPI SPCR. It would work the same as "earlycon" without
> extra options for early consoles.
>
> If you would want to make it explicit than I agree with Sergey
> and would prefer "console=spcr" instead of "console=auto".
I'm going with "console=spcr". FYI.
P.
>
> Note kernel tries to enable some consoles automatically even
> when "console" parameter is not defined at all. Therefore "auto"
> is somehow misleading.
>
> Best Regards,
> Petr
>
> PS: JFYI, I have vacation the following week...
>
