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From: "Michel Dänzer" <michel@daenzer.net>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 1/2] drm: Fix off-by-one in vblank hardware counter wraparound handling
Date: Wed, 27 May 2015 16:17:05 +0900	[thread overview]
Message-ID: <55656F71.1040704@daenzer.net> (raw)
In-Reply-To: <20150526114811.GL12971@phenom.ffwll.local>

On 26.05.2015 20:48, Daniel Vetter wrote:
> On Tue, May 26, 2015 at 05:53:38PM +0900, Michel Dänzer wrote:
>> From: Michel Dänzer <michel.daenzer@amd.com>
>>
>> dev->max_vblank_count contains the largest value that can be represented
>> by the hardware counter. When the hardware counter wraps around, we have
>> to add that value + 1 to get the same value as if the hardware counter
>> didn't wrap around.
>>
>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
> 
> Well there's two users of this really, one wants the max (this one here)
> and the other a mask.

Well, this one has been around much longer. :) Looks like drm_vblank_on
added a (probably valid, see below) assumption without updating the
field name to reflect that.


> And all the drivers use it as a mask.

How so? They just assign the value, which happens to work for both
meanings above in all cases.


> Maybe rename it to vblank_counter_mask or similar while at it to
> prevent further confusion?

I'm just fixing an off-by-one bug here; I invite you or anyone else to
be my guest for anything more. :)


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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  reply	other threads:[~2015-05-27  7:17 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-26  8:53 [PATCH 1/2] drm: Fix off-by-one in vblank hardware counter wraparound handling Michel Dänzer
2015-05-26  8:53 ` [PATCH 2/2] drm/radeon: Fix max_vblank_count value for current display engines Michel Dänzer
2015-05-28  4:17   ` Alex Deucher
2015-05-26  8:57 ` [PATCH 1/2] drm: Fix off-by-one in vblank hardware counter wraparound handling Christian König
2015-05-26 11:48 ` Daniel Vetter
2015-05-27  7:17   ` Michel Dänzer [this message]
2015-05-27 11:03     ` Daniel Vetter
2015-05-27  7:42   ` Ville Syrjälä

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