spi: Add DMA mode support to spi-qcom-qspi
Merge series from Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com>:
There are large number of QSPI irqs that fire during boot/init and later
on every suspend/resume.
This could be made faster by doing DMA instead of PIO.
Below is comparison for number of interrupts raised in 2 scenarios...
Boot up and stabilise
Suspend/Resume
Sequence PIO DMA
=======================
Boot-up 69088 19284
S/R 5066 3430
Speed test results...
spi-nor read times in sec after 2 min uptime
============================================
PIO - Iterations-1000, min=3.18, max=3.74, avg=3.53
DMA - Iterations-1000, min=1.21, max=2.28, avg=1.79
spi-nor write times in sec after 2 min uptime
=============================================
PIO - Iterations-1000, min=3.20, max=8.24, avg=3.58
DMA - Iterations-1000, min=1.25, max=5.13, avg=1.82
Further testing performed...
a) multiple entries in sgt (simulated by max_dma_len = 1024)
b) fallback to pio (simulated by dma setup failure)