Re: [PATCH/RFT] fbdev driver for HP Visualize FX cards

[Sven Schnelle <svens@stackframe.org>]

Thomas Zimmermann <tzimmermann@suse.de> writes:

> Hi
>
> Am 06.11.21 um 22:02 schrieb Sven Schnelle:
>> Thomas Zimmermann <tzimmermann@suse.de> writes:
>> 
>>> Hi
>>>
>>> Am 01.11.21 um 09:54 schrieb Sven Schnelle:
>>>> Hi Thomas,
>>>> Thomas Zimmermann <tzimmermann@suse.de> writes:
>>>> Thanks, i wasn't aware as i normally don't do any graphics related
>>>> development. I take a look at dri and port the driver, which is
>>>> hopefully not too hard.
>>>
>>> Sounds good.
>>>
>>> The one big difference when converting is that DRM really wants
>>> drivers to support 32-bit XRGB colors. It's not a DRM limitation per
>>> se, but a requirement of today's userspace programs. AFAICS your fbdev
>>> driver uses a 256-color palette format. So the DRM driver would have
>>> to convert
>>> XRGB8888 to 8-bit RGB332 and install a corresponding palette. Don't
>>> worry, it's easy. Take a look at the cirrus driver for a simple DRM
>>> driver. [1]
>> I have converted the driver, 
>
> Cool!
>
>> but am using FORMAT_C8 because i haven't
>> figured out yet how to switch the card to XRGB8888. That's still on the
>> TODO list.
>
> Don't worry. As I outlined , you can still convert any image from
> XRGB888 to RGB332 and display this instead.
>
>> One question about hw blitting: with the old fbdev framework one
>> could
>> replace the fb_imageblit function. For normal console text, this
>> function gets called with a monochrome bitmap, and an fg/bg color value.
>> This makes it easy to use HW accelerated blitting for text. In the
>> gpu/drm drivers i think i found only one driver (nouveau) doing this and
>> that was via the drm fbdev layer.
>> Is that still the way to go, or is there a better way to do HW
>> accelerated
>> text blitting?
>
> Simply call drm_fbdev_generic_setup() after registering the
> device. This should give you a console.

Yes, that's what i have, and it works. The only thing that is odd (and i'm
not sure whether that's a bug or not), is that fbset changes the
resolution of the framebuffer, but doesn't reprogram the hardware to the
new resolution. That means if i boot with 1920x1080 resolution, and do a
fbset -a 640x480-60, only a small part of the screen is used now, but
the physical resolution stays at 1920x1080. I first thought that's a bug
in my driver, but my x86 Thinkpad X1 with nouveau behaves the same.

> Don't bother about HW-accelerated blitting. From what I've heard, it
> barely makes a difference nowadays. And our generic helpers have
> plenty of features. Not using them to get a small benefit from HW
> blitting isn't worth it.

Not sure. With my first driver (the fbdev/fbcon one without drm), that
made a big difference when scrolling or the whole screen was updated. I
never measured it, but i would think it was a 1:10 ratio.

Regards
Sven