linux-kernel - RE: [PATCH v3] video: hyperv: hyperv_fb: refresh the VM screen by force on VM panic

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Message-ID: <EE124450C0AAF944A40DD71E61F878C98F6F78@SINEX14MBXC417.southpacific.corp.microsoft.com>
Date:	Thu, 31 Jul 2014 10:11:41 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"plagnioj@...osoft.com" <plagnioj@...osoft.com>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH v3] video: hyperv: hyperv_fb: refresh the VM screen by
 force on VM panic

> -----Original Message-----
> From: Tomi Valkeinen [mailto:tomi.valkeinen@...com]
> Sent: Wednesday, July 30, 2014 22:24 PM
> > +static struct fb_info *hvfb_info;
> 
> Static variables like these are usually a no-no. This prevents you from
> having multiple device instances.
I agree.

> >  static uint screen_width = HVFB_WIDTH;
> >  static uint screen_height = HVFB_HEIGHT;
> >  static uint screen_depth;
> >  static uint screen_fb_size;
> >
> > +/* If true, the VSC notifies the VSP on every framebuffer change */
> > +static bool synchronous_fb;
> > +
> 
> Same comment here.
> 
> However, if (and only if) the driver is already designed to work only
> with single device instance, then this patch is probably ok. But even
IMO the host should only provide at most 1 synthetic video device to a VM. :-)

> then, I'd prefer this to be handled without static variables so that the
> driver could eventually be changed to support multiple device instances.

Hi Tomi,
Maybe we can remove these static stuff:
+static struct fb_info *hvfb_info;
+static struct notifier_block hvfb_panic_nb = {
+	.notifier_call = hvfb_on_panic,
+};
by kmalloc()-ing  a new struct:
struct hv_fb_panic_nb {
        struct fb_info *hvfb_info;
        struct notifier_block nb;
}
?
I think in hvfb_on_panic() we should be able to get the
hvfb_info pointer by
hvfb_info = container_of(nb, struct hv_fb_panic_nb, nb).

If you like that or have a better idea, please let me know so
I can make a new patch.

Thanks,
-- Dexuan
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