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

[Thomas Zimmermann]

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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