On Mon, 2007-06-11 at 10:59 -0700, Jesse Barnes wrote: > The patch doesn't yet deal with two obvious cases (and probably more > that I'm missing, it's untested yet): > - the hardware counter resets on mode switch, we need to rebase > the appropriate last_counter at that point so it's not treated as > a counter wrap
I think this should be handled in the core by having an offset that
relates the hardware counter to the software visible value. Mode setting
would then 'rebase' the offset to make the user-visible value change
smoothly:
pre_mode_set
old = current raw hardware counter
post_mode_set
new = current raw hardware counter
offset += old - new
now create a 'cooked' hardware counter:
cooked hardware counter = offset + raw hardware counter
> - a client interested in signals but also blocked on a vblank event
> may cause vblanks to be disabled if it received signal at the wrong
> time
the core should track a per-crtc enable/disable count and call the
driver when it transitions through zero.
> + unsigned long last_vblank_count[2];
> + atomic_t vblank_count[2];
For a first implementation, I suggest that the driver never store this
value and just read from the registers every time it fetches the frame
counter. You could 'optimize' reading when the interrupt was running by
caching the last value, but this will be race-prone.
> + /*
> + * Now update the appropriate counter.
> + * Assume we haven't missed a full 24 bits of vblank
> + * events, or that it won't matter if they're not accounted
> + * for when we adjust for wrapping.
> + * FIXME: if count was zero'd due to modeset, need to rebase
> + */
> + spin_lock_irqsave(&dev->vbl_lock, irqflags);
> + if (count < dev_priv->last_vblank_count[crtc]) {
> + diff = 0xffffff - dev_priv->last_vblank_count[crtc];
> + diff += count;
> + } else {
> + diff = count - dev_priv->last_vblank_count[crtc];
> + }
> + dev_priv->last_vblank_count[crtc] = count;
> + spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
> + atomic_add(diff, &dev_priv->vblank_count[crtc]);
> + return atomic_read(&dev_priv->vblank_count[crtc]);
ick. just read the registers and return the value here. We should place
wrap-detection in the core code by reporting the range of the register
values; with the offset suggested above, that would result in a single
addition to convert from raw to cooked frame counts.
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