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

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Hi

Am 16.02.23 um 18:20 schrieb 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

Pun intended? :D


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.

Yeah, the attribute controller is *fun* to work with. In the next iteration, I'll probably add a helper to do all this; similar to bochs.

Best regards
Thomas



--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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