SPI operations on interrupt context!?

Hi all,

I'm dealing with a SPI driver and I have a doubt. I need to read and write
data to spi (registers and values) inside interrupt handler. I want to know
if this pattern is safe or if I'll face problems with it.

This code is being added to gpio-mcp23s08.c driver to handle IRQ and save
INTCAP at interruption time. INTCAP register keeps the input port status at
interruption time. I want to capture this as fast as possible and put it at
a circular queue. I write this code inspired by spi_sync function, but
using spinlocks so it doesn't sleeps. But, these spin_(un)lock calls seems
a bad ideia to me. Any better idea or guidelines?

Here is the code.
https://gist.github.com/gkos/4cce494e90518077084a#file-gpio-mcp23s08-c-L440

The functions are mcp23s17_read_irqsafe and mcp23s17_read_irqsafe_complete

PS: The code is a little messed up (because I've been trying to optimize
this INTCAP capturing by many means)

Cheers
- dhs

-- 
*"Do or do not. There is no try"*
  *Yoda Master*
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