Messages in this thread |  | | Subject | Re: [PATCH 1/3] drm: Widen vblank count to 64 bits. Change vblank time precision to ns | From | Michel Dänzer <> | Date | Thu, 6 Jul 2017 17:05:39 +0900 |
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On 06/07/17 04:45 PM, Michel Dänzer wrote: > 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.
BTW, this got me thinking that we should probably treat _DRM_VBLANK_NEXTONMISS the same way, i.e. clear the flag after updating vblwait->request.sequence. Otherwise there could theoretically (though unlikely) be an infinite loop:
ioctl with _DRM_VBLANK_NEXTONMISS, target missed => wait for next vblank wait interrupted by signal lather, rinse, repeat
I'd advise against adding a "next on miss" flag for the new ioctl until there is specific demand for that.
-- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer
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