linux-kernel - Re: [PATCH] serial: 8250: Default SERIAL_OF_PLATFORM to SERIAL

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Date:   Thu, 15 Nov 2018 09:19:14 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: 8250: Default SERIAL_OF_PLATFORM to SERIAL_8250



On 11/14/2018 9:38 PM, Guenter Roeck wrote:
> On Wed, Nov 14, 2018 at 07:56:47PM -0800, Florian Fainelli wrote:
>>
>>
>> On November 14, 2018 5:11:25 PM PST, Guenter Roeck <linux@...ck-us.net> wrote:
>>> On Thu, Nov 01, 2018 at 11:26:06AM -0700, Florian Fainelli wrote:
>>>> It is way too easy to miss enabling SERIAL_OF_PLATFORM which would
>>>> result in the inability for the kernel to have a valid console
>>> device,
>>>> which can be seen with:
>>>>
>>>> Warning: unable to open an initial console.
>>>>
>>>> and then:
>>>>
>>>> Run /init as init process
>>>> Kernel panic - not syncing: Attempted to kill init!
>>> exitcode=0x00000100
>>>>
>>>> Since SERIAL_OF_PLATFORM already depends on SERIAL_8250 && OF there
>>>> really is no drawback to defaulting this config to the value of
>>>> SERIAL_8250.
>>>>
>>>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>
>>> This patch results in situations where CONFIG_SERIAL_OF_PLATFORM is now
>>> defined where it was not previously. Example mpc85xx_defconfig. This in
>>> turn results in boot failures for those configurations, with an error
>>> message of
>>>
>>> of_serial: probe of e0004500.serial failed with error -22
>>>
>>> which wasn't seen before.
>>
>> Do you know which Device Tree is being used here? The most obvious thing that could be done is to add a !PPC condition but this might be missing other platforms doing their own 8250 registration yet being OF aware (sparc?).
>>
>>>
>>> Not sure if replacing a potential problem with a real one is really an
>>> improvement.`
>>
>> That comment is not particularly helpful though I have an appreciation for when a change breaks things in unexpected ways and how frustrating that can be.
> 
> Actally, never mind. I dropped the test cases. Sorry for the noise.

Why? The tests are useful, if I gave you an impression that I was just
going to walk away from this issue and not look at it, then that is not
happening. What I was objecting to is your qualification of the issue,
this is unfortunately not a potential/latent problem, it happens more
often than not.

The key difference is that most subsystems that are CONFIG_OF aware will
get that awareness enabled/active automatically, that is not the case
with the 8250 driver, which is why this you can shoot yourself in the
foot and end-up with the 8250 driver enabled, but not
CONFIG_SERIAL_OF_PLATFORM. I also suspect that for historical reasons
powerpc "manually" registers its 8250 ports and does not rely on
CONFIG_OF_SERIAL_PLATFORM.

I will try to cook a patch as quickly as possible. Thanks
-- 
Florian