[PATCH 0/2] spi: fsi: Reduce max transfer size to 8 bytes

David Laight David.Laight at ACULAB.COM
Sat Jul 17 23:46:15 AEST 2021

From: Eddie James
> Sent: 16 July 2021 14:39
> The security restrictions on the FSI-attached SPI controllers have
> been applied universally to all controllers, so the controller can no
> longer transfer more than 8 bytes for one transfer. Refactor the driver
> to remove the looping and support for larger transfers, and remove the
> "restricted" compatible string, as all the controllers are now
> considered restricted.

Aren't there significant performance (and device wear?) penalties
for doing short SPI eeprom writes?

IIRC (and I'm not getting my serial busses confused) a write request
can request an aligned transfer of up to (typically) 32 bytes.
At which point you need to wait for the status to indicate 'complete'.

So restricting writes to 8 bytes increases block write times
by a factor of 4.

Increasing the numbers of writes by a factor or 4 may also have
an effect on device wear - but that is more likely only affected
by erase cycles.


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