Re: [PATCH] s390/console: enable dummy console for vt

From: Christian Borntraeger
Date: Thu Feb 15 2018 - 06:56:59 EST

On 02/15/2018 12:26 PM, Geert Uytterhoeven wrote:
> Hi Christian,
>
> On Thu, Feb 15, 2018 at 12:14 PM, Christian Borntraeger
> <borntraeger@xxxxxxxxxx> wrote:
>> To enable the virtual terminal layer with virtio-gpu, we need to
>> provide the dummy console. This console is hidden behind CONFIG_IOMEM
>> via the graphics support. Instead of fully enabling the graphic
>> drivers lets just provide a Kconfig option for the dummy console.
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>> ---
>> New version: instead of moving around the graphic and console stuff,
>> let's just keep an s390 specific variant of CONFIG_DUMMY_CONSOLE
>> arch/s390/Kconfig | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
>> index cbe1d978693a..a69690f616f3 100644
>> --- a/arch/s390/Kconfig
>> +++ b/arch/s390/Kconfig
>> @@ -952,6 +952,11 @@ config S390_HYPFS_FS
>>
>> source "arch/s390/kvm/Kconfig"
>>
>> +config DUMMY_CONSOLE
>> + bool
>> + depends on VT
>> + default y
>> +
>> config S390_GUEST
>> def_bool y
>> prompt "s390 support for virtio devices"
>
> Really?
>
> You already have your own copy of HAS_IOMEM, which makes it hard for
> people to track which one applies where.
>

I am open for better suggestions. One idea that I had was to reverse
the logic in s390 (and use the common code HAS_IOMEM)

like


diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index cbe1d978693a..123dd593ea20 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -715,8 +715,8 @@ endif # PCI
config PCI_DOMAINS
def_bool PCI

-config HAS_IOMEM
- def_bool PCI
+config NO_IOMEM
+ def_bool y if !PCI

config IOMMU_HELPER
def_bool PCI


This would enable CONFIG_VT and also CONFIG_DUMMY_CONSOLE as long as
PCI is enabled. If DUMMY_CONSOLE is not enabled (e.g. due to missing PCI),
we get a crash in the VT layer as conswitchp is then null.

Somewhat tricky.