[U-Boot] [U-Boot, 5/8] rockchip: spi: only wait for completion, if transmitting

[Philipp Tomsich]

> The logic in the main transmit loop took a bit of reading the TRM to
> fully understand (due to silent assumptions based in internal logic):
> the "wait until idle" at the end of each iteration through the loop is
> required for the transmit-path as each clearing of the ENA register
> (to update run-length in the CTRLR1 register) will implicitly flush
> the FIFOs... transmisson can therefore not overlap loop iterations.
> 
> This change adds a comment to clarify the reason/need for waiting
> until the controller becomes idle and wraps the entire check into an
> 'if (out)' to make it clear that this is required for transfers with a
> transmit-component only (for transfers having a receive-component,
> completion of the transmit-side is trivially ensured by having
> received the correct number of bytes).
> 
> The change does not increase execution time measurably in any of my
> tests.
> 
> Signed-off-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>
> ---
> 
>  drivers/spi/rk_spi.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 

Applied to u-boot-rockchip, thanks!