linux-kernel - MMC host driver requirements

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Date:	Sun, 7 Sep 2008 23:52:28 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	linux-kernel@...r.kernel.org
Cc:	drzeus-mmc@...eus.cx, oakad@...oo.com
Subject: MMC host driver requirements

Hello,

I'm writing a driver for ENE CB710/720 memory card readers found in some
laptops (ie. some versions of HP Compaq nx9500). This chip has three
memory card interfaces: MMC/SD, SmartMedia, MemoryStick. I started with
the MMC interface as I have a card to test it with, but I could not find
any documentation about MMC stack besides the source code.

So here are some questions:

1. Can I call mmc_detect_change() after mmc_alloc_host() but before or
   during mmc_add_host() (ie. from interrupt handler)? If yes, what
   if mmc_alloc_host() fails then?
2. Can I call mmc_request_done() from ->request() handler?
3. Does MMC stack serialize calls to ->request() or any other host
   driver ops?
4. What is the difference (if any) between mrq->data and mrq->cmd->data
   as seen from ->request()?
5. Are there any constraints to scatterlist passed to ->request()
   - number of elements, data alignment, element data size?
   (At first I assumed that there are none and have writted a simple
   wrapper to guarantee multiple-of-16-byte data blocks - but maybe
   its just not needed?)

If/when I finish the driver there is the question what are the
requirements for it to be accepted to mainline? It's based on
reverse-engineering work on a Windows driver so it will have
some magic register-access sequences, as the original driver used
completely different MMC/SD stack and probably not fully used chip's
capabilities.

BTW, Google said nothing interesting about the hardware: most hits are
about not existing drivers for it and manufacturer ignoring inquiries
for datasheets.

Best Regards,
Michał Mirosław
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