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

On 02/15/2018 12:26 PM, Geert Uytterhoeven wrote:

Hi Christian,

On Thu, Feb 15, 2018 at 12:14 PM, Christian Borntraeger
[off-list ref] wrote:

quoted

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 <redacted>
---
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.