[PATCH 17/17] drm/cirrus: Use VGA macro constants to unblank

[Ville Syrjälä]

On Thu, Feb 16, 2023 at 02:21:43PM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 16.02.23 um 13:52 schrieb Ville Syrjälä:
> > On Thu, Feb 16, 2023 at 01:03:02PM +0100, Thomas Zimmermann wrote:
> >> Hi,
> >>
> >> thanks for taking a look at the patches.
> >>
> >> Am 16.02.23 um 12:33 schrieb Gerd Hoffmann:
> >>> On Wed, Feb 15, 2023 at 05:15:17PM +0100, Thomas Zimmermann wrote:
> >>>> Set the VGA bit for unblanking with macro constants instead of magic
> >>>> values. No functional changes.
> >>>
> >>> blank/unblank should work simliar to bochs (see commit 250e743915d4),
> >>> that is maybe a nice thing to add of you modernize the driver anyway.
> >> Yeah, it's the VGA PAS field. [1] But is it really called blanking? PAS
> >> controls palette access, but blanking is sounds more like DPMS.
> > 
> > Why aren't people just using the normal way of flipping the
> > screen off bit in sequencer register 01?
> 
> Setting the SD bit in SR01 isn't a bad idea. We can do this as part of 
> enabling/disabling the plane.
> 
> But for PAS, we don't have a choice. It's one of the bazillion obscure 
> VGA settings and (according to a comment in the source code) we need to 
> update it for compatibility.

Well, you do need to enable the palette to see something
other that border color. Not sure tha't a very obscure thing :P

On a related note, the code looks pretty sketchy. It just
blindly writes to 0x3c0 assuming it is the attribute controller
index register. But unless you explicitly reset the flip-flop
it could actually be the data write register instead. That could
easily happen if the previous access to the attribute controller
was a read since reads do not toggle the register role.

-- 
Ville Syrjälä
Intel