fuspi: Fix 'sleepable after non-sleepable' lock
With WITNESS enabled we see the following warning:
lock order reversal: (sleepable after non-sleepable) 1st 0xffffffd0847c7210 fu540spi0 (fu540spi0) @ /usr/home/kp/axiado/hornet-freebsd/src/sys/riscv/sifive/fu540_spi.c:297 2nd 0xffffffc00372bb30 Clock topology lock (Clock topology lock) @ /usr/home/kp/axiado/hornet-freebsd/src/sys/dev/extres/clk/clk.c:1137 stack backtrace: #0 0xffffffc0002a579e at witness_checkorder+0xb72 #1 0xffffffc0002a5556 at witness_checkorder+0x92a #2 0xffffffc000254c7a at _sx_slock_int+0x66 #3 0xffffffc00025537a at _sx_slock+0x8 #4 0xffffffc000123022 at clk_get_freq+0x38 #5 0xffffffc0005463e4 at __clzdi2+0x2bb8 #6 0xffffffc00014af58 at randomdev_getkey+0x76e #7 0xffffffc0001278b0 at simplebus_add_device+0x7ee #8 0xffffffc00027c9a8 at device_attach+0x2e6 #9 0xffffffc00027c634 at device_probe_and_attach+0x7a #10 0xffffffc00027d76a at bus_generic_attach+0x10 #11 0xffffffc00014aab0 at randomdev_getkey+0x2c6 #12 0xffffffc00027c9a8 at device_attach+0x2e6 #13 0xffffffc00027c634 at device_probe_and_attach+0x7a #14 0xffffffc00027d76a at bus_generic_attach+0x10 #15 0xffffffc000278bd2 at config_intrhook_oneshot+0x52 #16 0xffffffc000278b3e at config_intrhook_establish+0x146 #17 0xffffffc000278cf2 at config_intrhook_disestablish+0xfe
The clock topology lock can sleep, which means we cannot attempt to
acquire it while holding the non-sleepable mutex.
Fix that by retrieving the clock speed once, during attach and not every
time during SPI transaction setup.
Submitted by: kp
Sponsored by: Axiado