On Thu, Mar 30, 2017 at 2:03 PM, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > On Wed, Mar 22, 2017 at 09:56:12PM +0100, Daniel Vetter wrote: >> If we restrict this helper to only kms drivers (which is the case) we >> can look up the correct mode easily ourselves. But it's a bit tricky: >> >> - All legacy drivers look at crtc->hwmode. But that is update already >> at the beginning of the modeset helper, which means when we disable >> a pipe. Hence the final timestamps might be a bit off. But since >> this is an existing bug I'm not going to change it, but just try to >> be bug-for-bug compatible with the current code. This only applies >> to radeon&amdgpu. >> >> - i915 tries to get it perfect by updating crtc->hwmode when the pipe >> is off (i.e. vblank->enabled = false). >> >> - All other atomic drivers look at crtc->state->adjusted_mode. Those >> that look at state->requested_mode simply don't adjust their mode, >> so it's the same. That has two problems: Accessing crtc->state from >> interrupt handling code is unsafe, and it's updated before we shut >> down the pipe. For nonblocking modesets it's even worse. >> >> For atomic drivers try to implement what i915 does. To do that we add >> a new hwmode field to the vblank structure, and update it from >> drm_calc_timestamping_constants(). > > i915 clear crtc->hwmode.crtc_clock when turning the crtc off, which > this does not do for the new vblank->hwmode. I guess no one should > really end up in these codepaths with a disabled crtc, but parts of > drm_irq.c sort of look like they're expecting it to happen. > > So should we have some way to clear out the vblank->hwmode.crtc_clock > for disabled crtcs? And then maybe make some of these crtc_clock checks > WARN and eventually just nuke it all if it looks like nothing is hitting > those? So the trouble is that with a pile of dpms on/off/on/off you could run drm_crtc_vblank_on/off a lot, without ever calling the drm_calc_vbltimestamps helper again to re-upload the mode. So I don't think we can clear vblank->hwmode.crtc_clock unfortunately in drm_crtc_vblank_off. But what we could do (at least with atomic) is WARN in the vblank helper if it's called outside of drm_vblank_on/off ... Not sure how useful that is (it won't catch when a driver outright forgets to call these) or whether we have enough checks already. Would be a separate patch (can do ofc if we agree on what exactly). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
