Messages in this thread | | | Date | Fri, 22 Feb 2008 11:06:13 -0800 | From | David Brownell <> | Subject | Re: [spi-devel-general] [PATCH] atmel_spi: support zero length transfer |
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> > If the driver could not handle zero length transfer, then the driver > > should reject it (just like unsupported transfer mode). Then the > > behavior will be 'assert chip select and wait some time' or 'rejected > > by the driver'. > > This would be OK. It would not be hard to fix pxa2xx_spi, for example, > to reject zero-length transfers in DMA mode, as long as it is acceptable > to reject the message in mid-message.
Such "illegal message" rejection is best done early; "fail-fast". Mid-message rejection isn't wrong, but it's a rude policy.
It'd be best to fix pxa2xx_spi to not start zero-length DMAs.
> If it were necessary to scan a > whole message for zero-length transfers and refuse to queue an offending > message, then that adds burden to all messages.
Sanity checking messages as they're submitted is easy; and it's also the natural point for setting up DMA mappings (and making those cachelines available for better use).
- Dave
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