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

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Date:   Thu, 6 Jul 2017 16:45:10 +0900
From:   Michel Dänzer <michel@...nzer.net>
To:     Keith Packard <keithp@...thp.com>,
        Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank
 time precision to ns

On 06/07/17 07:10 AM, Keith Packard wrote:
> This modifies the datatypes used by the vblank code to provide both 64
> bits of vblank count and to increase the resolution of the vblank
> timestamp from microseconds to nanoseconds.
> 
> The driver interfaces have also been changed to return 64-bits of
> vblank count; fortunately all of the code necessary to widen that value
> was already included to handle devices returning fewer than 32-bits.
> 
> This will provide the necessary datatypes for the Vulkan API.
> 
> Signed-off-by: Keith Packard <keithp@...thp.com>

[...]

> @@ -1492,9 +1515,11 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
>  
>  	switch (vblwait->request.type & _DRM_VBLANK_TYPES_MASK) {
>  	case _DRM_VBLANK_RELATIVE:
> -		vblwait->request.sequence += seq;
> +		req_seq = seq + vblwait->request.sequence;
>  		vblwait->request.type &= ~_DRM_VBLANK_RELATIVE;

Subtle breakage here: vblwait->request.sequence must still get updated
for _DRM_VBLANK_RELATIVE, in case we're interrupted by a signal.


> @@ -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.


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