linux-kernel - Re: [PATCH] Revert "tty: serial: pl011: add ttyAMA for matching pl011 console"

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Message-ID: <49b62273-9645-5310-571a-326acdd35574@arm.com>
Date:   Wed, 1 Mar 2017 13:55:07 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Aleksey Makarov <aleksey.makarov@...aro.org>,
        linux-serial@...r.kernel.org
Cc:     Peter Hurley <peter@...leysoftware.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] Revert "tty: serial: pl011: add ttyAMA for matching pl011
 console"

On 01/03/17 13:01, Aleksey Makarov wrote:
> 
> 
> On 03/01/2017 03:59 PM, Robin Murphy wrote:
>> On 01/03/17 12:26, Aleksey Makarov wrote:
>>> The original patch makes condition always true, so it is wrong.
>>>
>>> This reverts commit aea9a80ba98a0c9b4de88850260e9fbdcc98360b.
>>
>> It seems fairly clear that the intent of the code merely warrants
>> s/||/&&/ - wouldn't it be more straightforward to just fix that?
> 
> No, I don't think so.  The description of the patch says that it fixes a problem
> of double printing the logs with SPCR and both console=ttyAMA and earlycon are specified
> on the command string.  That wrong patch does "fix" it, but introduces
> a regression with the regular case.
> 
> With s/||/&&/ it would not even 'fix' the described problem.

Ah, I see, so it's that this fundamental approach itself was flawed, but
the bug causing it to match nothing happened to hide the underlying
problem. It might be useful to call that out explicitly in the commit
log. FWIW the "enabling the main console reprints earlycon contents"
problem has also been present for a while in the non-ACPI case when
relying on stdout-path for both main console and earlycon in DT, i.e.
with just "earlycon" on the command line (it seems to be OK if you
specify "earlycon=pl011,..." or explicitly add "console=ttyAMA0").

Thanks,
Robin.

> 
> Thank you
> Aleksey Makarov
> 
>> Robin.
>>
>>> ---
>>>  drivers/tty/serial/amba-pl011.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
>>> index 8789ea423ccf..56f92d7348bf 100644
>>> --- a/drivers/tty/serial/amba-pl011.c
>>> +++ b/drivers/tty/serial/amba-pl011.c
>>> @@ -2373,7 +2373,7 @@ static int __init pl011_console_match(struct console *co, char *name, int idx,
>>>  	if (strcmp(name, "qdf2400_e44") == 0) {
>>>  		pr_info_once("UART: Working around QDF2400 SoC erratum 44");
>>>  		qdf2400_e44_present = true;
>>> -	} else if (strcmp(name, "pl011") != 0 || strcmp(name, "ttyAMA") != 0) {
>>> +	} else if (strcmp(name, "pl011") != 0) {
>>>  		return -ENODEV;
>>>  	}
>>>  
>>>
>>
>