Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns

From: "Michel Dänzer" <michel@daenzer.net>
To: Keith Packard <keithp@keithp.com>,
	Dave Airlie <airlied@redhat.com>, Daniel Vetter <daniel@ffwll.ch>
Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns
Date: Fri, 7 Jul 2017 11:05:21 +0900	[thread overview]
Message-ID: <7afd9048-ef07-1f72-72f3-d1d69d368f92@daenzer.net> (raw)
In-Reply-To: <f57962d7-8741-a455-fc37-09c50c04e902@daenzer.net>

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On 07/07/17 10:34 AM, Michel Dänzer wrote:
> On 07/07/17 12:04 AM, Keith Packard wrote:
>> Michel Dänzer <michel@daenzer.net> writes:
>>
>>>> @@ -317,6 +317,9 @@ int via_driver_irq_postinstall(struct drm_device *dev)
>>>>  	if (!dev_priv)
>>>>  		return -EINVAL;
>>>>  
>>>> +	if (dev->driver->get_vblank_counter)
>>>> +		dev->max_vblank_count = 0xffffffff;
>>>
>>> What's the purpose of this? All drivers providing get_vblank_counter
>>> should already initialize max_vblank_count correctly.
>>
>> Yeah, I couldn't prove that this driver did that,
> 
> Which driver?
> 
>> and as Daniel says, we haven't ever audited the drivers to make sure
>> they do.
> 
> I don't think that's what he meant, rather that with the change above,
> all drivers have to be audited to make sure the added assignment doesn't
> clobber an earlier assignment by the driver.

... and if there are any drivers that set
dev->driver->get_vblank_counter but don't set dev->max_vblank_count to a
non-0 value, that the hardware counter actually has 32 bits.

I'd say don't bother, just drop this hunk.

-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer

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