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SubjectRE: [PATCH RFC] video: Add Hyper-V Synthetic Video Frame Buffer Driver
Date
> -----Original Message-----
> From: Olaf Hering [mailto:olaf@aepfle.de]
> Sent: Tuesday, February 19, 2013 11:51 AM
> To: Haiyang Zhang
> Cc: FlorianSchandinat@gmx.de; linux-fbdev@vger.kernel.org; KY Srinivasan;
> jasowang@redhat.com; linux-kernel@vger.kernel.org;
> devel@linuxdriverproject.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

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