linux-kernel - [PATCH 00/02] 32-bit PIO wrappers for scatterlists

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Message-ID: <20090206204343.GA13217@rere.qmqm.pl>
Date:	Fri, 6 Feb 2009 21:43:44 +0100
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Jens Axboe <axboe@...nel.dk>, Pierre Ossman <drzeus-mmc@...eus.cx>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 00/02] 32-bit PIO wrappers for scatterlists

Hello,

While writing a driver for CB710 MMC host I had to implement PIO routines
that transferred data to/from buffers described by scatterlists. As it
turned later this scheme is needed for similar devices that can't handle
[scatter-gather] DMA in hardware.

Following is my implementation of such routines that should be generic
enough to use in drivers doing PIO by 32-bit accesses (PCI based devices
or maybe other 32-bit word based busses).

Current implementation has some limitations:
1. it advances scatterlist iterator always by multiple of 4 bytes
2. it silently inserts zeroes after last byte of buffer when transferring
   data to the device (that's actually a good thing for my driver)
3. it silently ignores data that does not fit into specified buffer when
   transferring data from the device (this also is a good thing for the
   driver I wrote)

What those points mean is that driver writer has to know how many bytes
there are available in the buffer if its important, and has to use
multiple-of-4 transfer sizes when doing more than one transfer using
a single iterator.

Patches are against vanilla kernel 2.6.28.

Best Regards,
Michał Mirosław
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