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

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Message-ID: <53DA46C3.9080905@ti.com>
Date:	Thu, 31 Jul 2014 16:38:11 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Dexuan Cui <decui@...rosoft.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

On 31/07/14 13:11, Dexuan Cui wrote:
>> -----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.

To be honest, I haven't been using notifiers much. But the above looks
ok to me.

Or maybe you can add the notifier_block and the synchronous_fb to
hvfb_par? From the notifier_block pointer you could then get hvfp_par,
and from there hvfb_info.

 Tomi



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