spi: meson-spicc: add local pow2 clock ops to preserve rate between messages

spi: meson-spicc: add local pow2 clock ops to preserve rate between messages

commit 09992025dacd258c823f50e82db09d7ef06cdac4 upstream.

At the end of a message, the HW gets a reset in meson_spicc_unprepare_transfer(),
this resets the SPICC_CONREG register and notably the value set by the
Common Clock Framework.

This is problematic because:
- the register value CCF can be different from the corresponding CCF cached rate
- CCF is allowed to change the clock rate whenever the HW state

This introduces:
- local pow2 clock ops checking the HW state before allowing a clock operation
- separation of legacy pow2 clock patch and new enhanced clock path
- SPICC_CONREG datarate value is now value kepts across messages

It has been checked that:
- SPICC_CONREG datarate value is kept across messages
- CCF is only allowed to change the SPICC_CONREG datarate value when busy
- SPICC_CONREG datarate value is correct for each transfer

This didn't appear before commit 3e0cf4d3fc29 ("spi: meson-spicc: add a linear clock divider support")
because we recalculated and wrote the rate for each xfer.

Fixes: 3e0cf4d3fc29 ("spi: meson-spicc: add a linear clock divider support")
Reported-by: Da Xue <da@libre.computer>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220811134445.678446-1-narmstrong@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>