linux-kernel - Re: [PATCH v3 1/3] Kconfig : Remove HAS_IOMEM dependency for Graphics support

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Date:   Wed, 21 Feb 2018 11:39:12 -0500
From:   Farhan Ali <alifm@...ux.vnet.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     Thomas Huth <thuth@...hat.com>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-fbdev@...r.kernel.org,
        geert@...ux-m68k.org, tomi.valkeinen@...com,
        b.zolnierkie@...sung.com
Subject: Re: [PATCH v3 1/3] Kconfig : Remove HAS_IOMEM dependency for Graphics
 support



On 02/21/2018 07:11 AM, Christian Borntraeger wrote:
> 
> 
> On 02/21/2018 01:07 PM, Cornelia Huck wrote:
> [...]
>>>> But if you need to enable PCI to get IOMEM, I wonder why this patch here
>>>> is needed at all? The Graphics menu / VT dummy console should be
>>>> available in the config if IOMEM is enabled anyway?
>>>
>>> That is a good question. With CONFIG_PCI=y I can select virtio-gpu and dummy-console.
>>> IIRC the issue was that with patch 3 we can have the situation where we have
>>> CONFIG_VT = y and CONFIG_DUMMY_CONSOLE=n and this will crash early during boot as
>>> conswitchp is NULL.

Yes, VT layer initializes very early in the boot process and looks for a 
console. If it can't find any it will crash. I believe that was the 
whole point of having the dummy console.

>>
>> So in practice, CONFIG_VT depends on "there's a console available, even
>> if it's only the dummy one"?
> 
> Yes. Maybe we should simple move dummy_console outside of drivers/video/console/Kconfig
> into something that is always available.
> 

I agree, but where should it go? consoles are kinda tightly tied to 
video/Graphics Support.

>>
>>> This patches goal was to always enable dummy console even without
>>> PCI, but it obviously fails to do so.
>>
This patch should enable the dummy console even without PCI but we won't 
have DRM/Virtio GPU.

>> OTOH, the dummy console really should not depend on anything, as it is
>> only doing dummy things.
>>
>>>
>>> So what about allowing CONFIG_VT on s390 only if we have PCI?
>>>
>>>
>>> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
>>> index 84810075a6a0..1c7fe09d6f90 100644
>>> --- a/drivers/tty/Kconfig
>>> +++ b/drivers/tty/Kconfig
>>> @@ -11,7 +11,7 @@ if TTY
>>>   
>>>   config VT
>>>          bool "Virtual terminal" if EXPERT
>>> -       depends on !UML
>>> +       depends on !UML && (!S390 || PCI)
>>>          select INPUT
>>>          default y
>>>          ---help---
>>>
>>
>> Would cover your use case, but feels wrong to me... config dependencies
>> aren't fun :/
>>