linux-kernel - RE: [PATCH RFC] video: Add Hyper-V Synthetic Video Frame Buffer Driver

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Date:	Tue, 19 Feb 2013 17:48:39 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	Olaf Hering <olaf@...fle.de>
CC:	"FlorianSchandinat@....de" <FlorianSchandinat@....de>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	KY Srinivasan <kys@...rosoft.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: RE: [PATCH RFC] video: Add Hyper-V Synthetic Video Frame Buffer
 Driver

> -----Original Message-----
> From: Olaf Hering [mailto:olaf@...fle.de]
> Sent: Tuesday, February 19, 2013 11:51 AM
> To: Haiyang Zhang
> Cc: FlorianSchandinat@....de; linux-fbdev@...r.kernel.org; KY Srinivasan;
> jasowang@...hat.com; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org
> Subject: Re: [PATCH RFC] video: Add Hyper-V Synthetic Video Frame Buffer
> Driver
> 
> On Fri, Feb 15, Haiyang Zhang wrote:
> 
> > @@ -508,6 +544,18 @@ static int __init vesafb_init(void)
> >  	int ret;
> >  	char *option = NULL;
> >
> > +#if IS_ENABLED(CONFIG_HYPERV_FB)
> > +	/*
> > +	 * On Hyper-V both the emulated and synthetic video devices are
> > +	 * available. To avoid conflicts, we disable vesafb for the
> emulated
> > +	 * video if hyperv_fb is configured.
> > +	 */
> > +	if (is_hyperv()) {
> > +		pr_info("Disabled vesafb on Hyper-V.\n");
> > +		return -ENODEV;
> > +	}
> > +#endif
> 
> What is the reason for this hook? Is it not possible to claim the
> display like its appearently done by other drivers (like radeonfb can
> take over display from vesafb)?

The emulated video device is a separate device from the synthetic video.
The synthetic driver can only take control of the synthetic video, but not
the emulated video.

Actually, we already have a similar mechanism in ata/ata_piix.c to disable
emulated IDE drive on Hyper-V, so it won't conflict with the synthetic drive.

Thanks,
- Haiyang