make fbdev/fbcon switchable per driver?

[Daniel Vetter]

On Fri, Jan 27, 2017 at 11:00:38AM +0100, Gerd Hoffmann wrote:
>   Hi folks,
> 
> Problem at hand:  A virtual machine, equipped with two display devices,
> one virtual, one physical (using pci pass-through, or kvmgt-based vgpu).
> 
> There is no easy way for the user to configure which of the two display
> devices fbcon should run on.  i915 happens to win over bochs-drm or qxl,
> so you can't use the emulated gfx device as text console.
> 
> One way out would be to add a module option to each driver, to turn off
> fbdev emulation.  Attached patch does that for i915.
> 
> Comments?  Better ideas?

fbcon can be switched between different fbdev afaik, but don't ask me how.
I'd say if you want to keep fbcon (and not switch to something like
kmscon), then that's where this logic should be. Might even exist already.
Having a per-driver knob won't work, since then the next person complains
about his multi-amd setup using the wrong gpu :-)
-Daniel

> 
> cheers,
>   Gerd
> 

> From 19236e412a6f0e9390c1ce77d8702bbdb5511174 Mon Sep 17 00:00:00 2001
> From: Gerd Hoffmann <kraxel at redhat.com>
> Date: Fri, 27 Jan 2017 08:05:40 +0100
> Subject: [PATCH] drm i915: add fbdev option
> 
> Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 3e3632c..cc0ba3e 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -45,6 +45,11 @@
>  #include <drm/i915_drm.h>
>  #include "i915_drv.h"
>  
> +static bool enable_fbdev = true;
> +module_param_named(fbdev, enable_fbdev, bool, 0600);
> +MODULE_PARM_DESC(fbdev,
> +		 "Enable legacy fbdev emulation [default=true]");
> +
>  static int intel_fbdev_set_par(struct fb_info *info)
>  {
>  	struct drm_fb_helper *fb_helper = info->par;
> @@ -706,6 +711,9 @@ int intel_fbdev_init(struct drm_device *dev)
>  	struct drm_i915_private *dev_priv = to_i915(dev);
>  	int ret;
>  
> +	if (!enable_fbdev)
> +		return 0;
> +
>  	if (WARN_ON(INTEL_INFO(dev)->num_pipes == 0))
>  		return -ENODEV;
>  
> @@ -747,6 +755,8 @@ void intel_fbdev_initial_config_async(struct drm_device *dev)
>  {
>  	struct intel_fbdev *ifbdev = to_i915(dev)->fbdev;
>  
> +	if (!ifbdev)
> +		return;
>  	ifbdev->cookie = async_schedule(intel_fbdev_initial_config, ifbdev);
>  }
>  
> -- 
> 1.8.3.1
> 

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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch