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: Thu, 6 Jul 2017 16:45:10 +0900	[thread overview]
Message-ID: <83a2dbe9-dfcb-e31e-fc7b-14c4364daea5@daenzer.net> (raw)
In-Reply-To: <20170705221013.27940-2-keithp@keithp.com>

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@keithp.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