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Message-Id: <20080222190613.0043B229B4D@adsl-69-226-248-13.dsl.pltn13.pacbell.net> Date: Fri, 22 Feb 2008 11:06:13 -0800 From: David Brownell <david-b@...bell.net> To: nforrester@...i.edu, anemo@....ocn.ne.jp Cc: spi-devel-general@...ts.sourceforge.net, marc.pignat@...s.ch, linux-kernel@...r.kernel.org Subject: Re: [spi-devel-general] [PATCH] atmel_spi: support zero length transfer > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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