Re: [PATCH 0/8] fbdev: sm712fb: implement 2D acceleration w/ cleanups.

[Daniel Vetter]

On Sat, Feb 02, 2019 at 02:16:40PM +0800, Yifeng Li wrote:
> Previously, in staging/sm7xxfb (now fbdev/sm712fb), 2D acceleration
> was implemented, but after its submission, a critical bug that causes
> total system hang was discovered, as a stopgap measure, 2D ops was
> completele removed in commit 3af805735a25 ("staging: sm7xx: remove the
> buggy 2D acceleration support") and never implemented again.
> 
> It created a massive usability problem - on YeeLoong 8089, a notable
> MIPS platform which uses SM712 - even scrolling a single line of text
> on the console required an unaccelerated screen redraw, running "dmesg"
> typically takes 8-11 seconds, and absurdly, printf(), became a significant
> performance bottleneck that slows down GCC and "make", make the computer
> largely unusable.
> 
> So I decided to take a look. Most of the my actual development was done
> in 2014 in a personal out-of-tree driver, I did not mainline it because
> 2D acceleration was not working properly in 24-bit color. I discovered
> the solution in early 2019 and now it's ready to be mainlined.
> 
> This commit reimplements the 2D acceleration for sm712fb. Unlike the
> original implementation, which was messy and unnecessarily complicated
> by calling a 2D acceleration wrapper file with many unneeded functions,
> this is a minimum and (relatively) clean implementation. My tests have
> shown that running "dmesg" only takes 0.9 seconds, a performance boost
> of 950%. System hangs did not occur in my tests.
> 
> Currently, 2D acceleration is only supported on SM712 with little-endian
> CPUs, it's disabled on Big Endian systems and SM720 chips as a safety
> measure, since I code for myself without any monetary or hardware support
> from any company or OEMs, I don't have the hardware and it's completely
> untested. I should be also to purchase a Big Endian test platform and add
> proper support soon.  If you have a Big-Endian platform with SM7xx
> available for testing, please send an E-mail to me immediately! Thanks!
> 
> Also, thanks to Miodrag Vallat and other OpenBSD developers, this work
> would be impossible without their code, that served as a reference
> implementation for me.
> 
> Finally, during the development and testing of 2D acceleration, the
> modesetting code of this driver received a minor cleanup, and many
> issues about issues about the modesetting code and this driver in
> general have been documented.
> 
> Yifeng Li (8):
>   fbdev: sm712fb: update copyright headers.
>   fbdev: sm712fb: use type "u8" for 8-bit I/O.
>   fbdev: sm712fb: add 2D-related I/O headers and functions.
>   fbdev: sm712fb: support 2D acceleration on SM712 w/ Little-Endian CPU.
>   fbdev: sm712fb: add 32-bit color modes, drops some other modes.
>   Documentation: fb: sm712fb: add information mainly about 2D.
>   fbdev: sm712fb: Kconfig: add information about docs.
>   MAINTAINERS: sm712fb: list myself as one maintainer.

Since you care about this driver, considered converting it to a drm
display driver? You can still have all the acceleration and stuff, the
fbdev compat mode in drm is rather flexible.
-Daniel

> 
>  Documentation/fb/sm712fb.txt  | 123 +++++++-
>  MAINTAINERS                   |   1 +
>  drivers/video/fbdev/Kconfig   |   4 +
>  drivers/video/fbdev/sm712.h   | 129 +++++++-
>  drivers/video/fbdev/sm712fb.c | 574 ++++++++++++++++++++++++++--------
>  5 files changed, 679 insertions(+), 152 deletions(-)
> 
> -- 
> 2.20.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch