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From: David Laight <David.Laight@ACULAB.COM>
To: 'Eddie James' <eajames@linux.ibm.com>, "linux-spi@vger.kernel.org"
 <linux-spi@vger.kernel.org>
Subject: RE: [PATCH 0/2] spi: fsi: Reduce max transfer size to 8 bytes
Thread-Topic: [PATCH 0/2] spi: fsi: Reduce max transfer size to 8 bytes
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Date: Sat, 17 Jul 2021 13:46:15 +0000
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From: Eddie James
> Sent: 16 July 2021 14:39
>=20
> 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.

=09David

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