linux-kernel - Re: [PATCH v5 3/6] ACPI: parse SPCR and enable matching console

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Message-ID: <56F17B0B.306@linaro.org>
Date:	Tue, 22 Mar 2016 20:04:11 +0300
From:	Aleksey Makarov <aleksey.makarov@...aro.org>
To:	Peter Hurley <peter@...leysoftware.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	Russell King <linux@....linux.org.uk>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	Al Stone <ahs3@...hat.com>,
	Christopher Covington <cov@...eaurora.org>,
	Yury Norov <ynorov@...iumnetworks.com>,
	"Zheng, Lv" <lv.zheng@...el.com>, Jiri Slaby <jslaby@...e.com>
Subject: Re: [PATCH v5 3/6] ACPI: parse SPCR and enable matching console



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
>> <aleksey.makarov@...aro.org> 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