This problem was found on sg2042 server platform with the litmus test.
This patch is based on Guo Ren's patch [1].
[1] c53925298d
riscv: qspinlock: errata: Add ERRATA_THEAD_WRITE_ONCE fixup
The early version of T-Head C9xx cores has a store merge buffer
delay problem. The store merge buffer could improve the store queue
performance by merging multi-store requests, but when there are not
continued store requests, the prior single store request would be
waiting in the store queue for a long time. That would cause
significant problems for communication between multi-cores. This
problem was found on sg2042 & th1520 platforms with the qspinlock
lock torture test.
So appending a fence w.o could immediately flush the store merge
buffer and let other cores see the write result.
This will apply the WRITE_ONCE errata to handle the non-standard
behavior via appending a fence w.o instruction for WRITE_ONCE().
Signed-off-by: haijiao.liu@sophgo.com <haijiao.liu@sophgo.com>
4826e4f743