Subject: [PATCH v5 3/6] ACPI: parse SPCR and enable matching console

From: [email-masked] (Aleksey Makarov)
Date: Tue, 22 Mar 2016 20:04:11 +0300

On 03/22/2016 07:07 PM, Peter Hurley wrote:
> On 03/22/2016 04:09 AM, Andy Shevchenko wrote:
>> On Tue, Mar 22, 2016 at 12:46 PM, Aleksey Makarov
>> <[email-masked]> wrote:

>>> +       sprintf(opts, "%s,%s,0x%llx,%d", uart, iotype,
>>> +               table->serial_port.address, baud_rate);
>>
>> You may use snprintf(), though my question here what would happen on
>> 32-bit kernel when you supply 64-bit address as an option?
> 
> Yeah this should probably use %pa for the printf specifier.
> 
> But note this exposes underlying bug in the earlycon support, because
> that was originally written without 32/64-mixed bitness in mind; ie.,
> the address is parsed and handled as unsigned long in most places.

I don't quite follow this.  table->serial_port.address is explicitly u64,
not pointer, so, according to printk-formats.txt %llx is ok here, %pa is wrong.
Am I missing something?

>>>         /*
>>> -        * Just 'earlycon' is a valid param for devicetree earlycons;
>>> -        * don't generate a warning from parse_early_params() in that case
>>> +        * Just 'earlycon' is a valid param for devicetree and ACPI SPCR
>>> +        * earlycons; don't generate a warning from parse_early_params()
>>> +        * in that case
>>>          */
>>> -       if (!buf || !buf[0])
>>> -               return early_init_dt_scan_chosen_serial();
>>> +       if (!buf || !buf[0]) {
>>> +               init_spcr_earlycon();
>>
>>> +               early_init_dt_scan_chosen_serial();
>>> +               return 0;
>>
>> And you hide an error?
> 
> Well, this is a little bit tricky because "earlycon" early parameter with
> missing /chosen/stdout-path node is no longer an error, since ACPI may be
> specifying the earlycon instead.

Agree, but note the email by Rob Herring.  The code should be like this:

if (!buf || !buf[0]) {
	if (acpi_disabled) {
		return early_init_dt_scan_chosen_serial();
	} else {
		init_spcr_earlycon();
		return 0;
	}
}

But that requires to have made ACPI/DT decision at this point.

Thank you
Aleksey