Hi Dave,

On Fri, Dec 9, 2016 at 1:08 AM, Dave Airlie [off-list ref] wrote:

On 9 December 2016 at 07:28, Benjamin Herrenschmidt
[off-list ref] wrote:

quoted

On Thu, 2016-12-08 at 11:10 +0100, Daniel Vetter wrote:

quoted

quoted

With drmfb you basically have to shadow everything into memory & copy
over everything, and locks you out of simple 2D accel. For a simple text
console the result is orders of magnitude slower and memory hungry than
a simple fbdev.

Not true, we have full fbdev emulation, and drivers can implement the 2d
accel in there. And a bunch of them do. It's just that most teams decided
that this is pointless waste of their time.j

Ok so my knowledge might be outdated here. I was complaining to Dave about
how cirrusdrmfb didn't even use blits for fbcon scrolling and always double
buffered everything, and Dave made the point that you basically had to do
that for security reasons that I mostly forgot the details of.

It looks like bochsdrmfb and astdrmfb are the same. If things have changed,
then cool. Can you point me to a drmfb driver that is a good (and not too
complex) example with simple 2d accel ? I'm thinking mostly of color
expansion, bitblt and solid fill for fbcon, the way I used to do it in
radeonfb for example.

What are people using fbcon for that needs acceleration, this is where I get
a bit lost.

It's a console, if you aren't sshing into the machine.

It's main purpose should just be for gathering oopses and you've a lot better
chance of getting an oops if you don't have some sketchy gpu accel in the way.

Unless you're using the console as a text console, and don't run e.g. X on top.

The acceleration that most of the 2D things provide isn't ever that
great, and shadowing is a lot more effective if done properly. It's a feature
that kernel ppl obsess over but I don't get a lot of real world feedback,
(booting 9000 scsi nodes with debug on takes a long time was possibly
something I heard once, and I think we resolved).

It all depends on the complex balance between GPU performance, CPU performance,
CPU-to-frame buffer bandwidth, and amount of available system RAM.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds