SPI tranfer from a DSR

[Andrew Parlane <andrewp@xxxxxxxxxxxx>]

Hi,

I'm trying to write a driver for an NXP SC16IS740 SPI / I2C UART chip: 
http://www.nxp.com/documents/data_sheet/SC16IS740_750_760.pdf

I'm running on an AT91SAM7X512 (custom board), using the SPI interface.

When an interrupt occurs on the NXP chip, it asserts a GPIO line 
connected to the IRQ0 pin on the sam7. I've set up an interrupt handler 
for this in my driver. However when this occurs I need to perform an SPI 
transfer to read the IIR register to figure out what the interrupt is.

However in the ECOS reference on the SPI interface page: 
http://ecos.sourceware.org/docs-3.0/ref/spi-api.html It states that an 
SPI transfer should not be performed in an ISR or a DSR, for locking 
reasons and also we don't want to block a DSR.

So ideally we want to be able to start the transfer and then return from 
the DSR and get interrupted again when the transfer had finished.

Is there a nice way to do this without modifying the AT91 SPI driver?

Thanks,
Andrew


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