[PATCH 1/3] spi/qspi: Add memory mapped read support.

[Gupta, Pekon]

> From: Trent Piepho
> Are there any numbers to show if memory mapped read support is a
> benefit in Linux?  There is some question as to whether it's useful at
> all or not.
> 
> If it is, I think low latency for small reads is probably one of the
> only advantages.  To do that, you aren't going to want to deal with
> device PM for every single read.  It would make more sense to turn the
> hardware on when the MTD device is opened and leave it on until
> closed.
> 
+1

Therefore early suggestions were to make 'MM_MODE' as default
(if device enables it via DT). This means:
(1) switch to 'SPI_MODE' _only_ when required for commands like
 mtd_erase, etc. and switch back to 'MM_MODE' when done.
(2) And keep your controller clocks on.

This would ensure that you do minimum config-switching when using
MM_MODE. And would thus achieve low latency, and no driver intervention.

Yes, real thruput numbers would help clear the picture here ..

with regards, pekon