v2: - Also implement 2D acceleration for SM720.
- Remove writel_relaxed() and an explicit memory barrier, on MIPS, PowerPC and x86, relaxed writes do not have additional performance, and complicates the code.
- Document additional issues in the driver.
NOTE:
- This patchset should be applied after "[PATCH 0/8] fbdev: sm712fb: fix a series of lockups, crashes and gliches" (*), as it contains important fixes for issues in the original driver.
- This patchset has been tested by the author for SM712 and SM720, on MIPS and x86 without problem.
(*) https://marc.info/?l=linux-fbdev&m=155277512210375&w=2
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 little-endian CPUs, it's disabled on Big Endian systems 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.
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, many identified existing issues in driver in general have been documented.
Yifeng Li (7): 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.
Documentation/fb/sm712fb.txt | 129 +++++++- MAINTAINERS | 1 + drivers/video/fbdev/Kconfig | 4 + drivers/video/fbdev/sm712.h | 109 ++++++- drivers/video/fbdev/sm712fb.c | 551 +++++++++++++++++++++++++--------- 5 files changed, 642 insertions(+), 152 deletions(-)