mc13xxx: Define maximum SPI clock frequency global to driver

[Alexander Kurz]

Hi,
I just ran into a problem resulting from patch 6e18b3a48ee4
("mc13xxx: Define maximum SPI clock frequency global to driver").

On a kindle2 board the SPI communication between an iMX31 and a MC13783 
won't work at 20MHz. Unfortunately both ICs are BGA mounted blocking any 
access with scope probes. Attempts to tweak the pad properties to
PAD_CTL_DRV_HIGH | PAD_CTL_SRE_FAST | PAD_CTL_100K_PU
did not solve the problem - anyway this is a battery powered device where
the original implementers took great care on long battery life,
e.g. PAD_CTL_DRV_HIGH should not be nessesary for PMIC control.

I do not see any way to override the 20MHz bitrate from board code, and 
since the PMIC access is not time critical on an ebook-reader my choice
would be rather 200kHz.

Is there any way to override the driver supplied default max_speed_hz?
If not, my proposal is to either
* revert this patch and let the board code choose frequency
or
* reduce the speed to some common acceptable rate, e.g. 6MHz are fine

How was this solved with other SPI devices?

Cheers, Alexander