The Qualcomm Universal Peripherals Engine (QUP) is a unified SPI and I2C
peripheral that ships with a variety of Qualcomm SoCs.
It supports three transfer modes - single PIO, block PIO and DMA.
This driver only supports the single PIO mode, which is enough to
bootstrap the rest of the SPI NAND/NOR support and means I can do
things like read the Wifi calibration data from NOR. It has some
hardware support code for the other transfer modes as well as
some support for split transfers (ie, transfers with no read or
write phase), but I haven't yet implemented those.
This driver is based on four sources - the linux driver, the u-boot
driver, some initial work done for APQ8064 by mmel@, and the APQ8064
Technical Reference Manual which is surprisingly free and open to
read. The linux and u-boot drivers approach a variety of things
completely differently, from how PIO is done, the hardware support
for re-ordering bytes in a transfer word and how the CS lines
are used.
Tested:
* IPQ4018, SPI to NAND/NOR flash, PIO only
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