On Tue, Feb 07, 2006 at 11:28:16AM +0100, Alexander Nassian wrote:
> Hi,
>
> I'm new to kernel programming and wanted to try to develop my first "real"
> kernel module. Up to now I only programmed little, useless, modules to get
> into the kernel.
>
> Because there is no module for the Ricoh Memory Host Adapter, which is in my
> notebook, I want to start developing one.
> 00:0a.2 Class 0805: Ricoh Co Ltd R5C822 SD/SDIO/MMC/MS/MSPro Host Adapter (rev 17)
>
> The problem is, that I have absolutely no idea where to start. When I'm
> looking at the code of existing MMC modules, I wanna start cry.
Do you have documentation for that chip ?
If not, can you get it ?
I found Ricoh LSI's pages easily enough, and there are no deep documentation
available for this chip for direct download:
http://www.ricoh.com/LSI/product_pcif/pcc/5c821/index.html
If I had hardware where this chip exists, I would do following:
- Contact vendor directly, and ask for necessary documentation
and other support, under a limited scope NDA if necessary,
so that I can create device driver for it to be used in Linux
system. Plus tell that:
- Documentation and support I receive from vendor under the NDA
will not be made publically available, nor privately unless
vendor informs me otherwise (e.g. introduces some other named
individual/company looking/working for the same and that the
vendor is explicitely allowing me to tell my info to them.)
- I would prefer not to receive Windows driver sources as
an example of how to program the chip; such would endanger
entire Open Source driver development.
- NDA (scope) limitation is about:
- Documentation redistribution, including extensive copying
to public material.
- NDA has expiration time, after which it no longer binds
(say: 1 to 5 years)
- Possible penalty values are sensible when talking about
individuals (e.g. USD 10k, not million(s) - sums that do
hurt individual hobby programmer a lot, and make to think
about what to release publically. )
- Resulting source code will be minimally informative about what
is going on in spots that are vendor hardware specific (e.g.
other than generic PCI interface stuff.) And if the vendor wants,
they can review the source code for the (lack of) public
hardware specific informativity before release.
When some control register needs manipulation in these private
parts, values stored there are hex literals, and not #define:d
mnemonics. When processing logic affects values (e.g. by mode)
one can always deduct changes in bit-patterns to mean something,
and obfuscation can not completely hide everything.
E.g. where some "deep magic" is needed, that is documented at
most with
"Doc 5: part 3.2.1"
and somewhere in beginning comments:
"Doc 5: R5C821 programming documentation errata 3 received under NDA"
- Code shall be _maintainable_ (to track possibly changing kernel
API conventions within Linux,) preferrably without original
author and NDA documents. In essence this means separation
of vendor hardware specific code to internal procedures and
to use internal datastructures in its handling. Mapping
from external to internal shall ne via easily maintainable
interfaces.
- Preferrably there shall be no "this internal driver is only
available in pre-compiled object-file format" -- Linux exists
now in considerably large number of possible processors, and
it makes things a lot easier, if there is no need to supply
pre-compiled binary libraries to all of them.
- If the vendor does not answer, then trying via near-by sales
representative, who usually speaks your language.
Getting thru them with an idea that it would be productive for
them to help you while you are not buying their products might
take some talking, though...
> Do you have any tips, tutorials, ... how I can start, step by step, the
> development of this module?
"Writing device drivers for Linux" or some such titled book..
You can receive support for Linux side driver interfaces, especially
if there is no matured device interface for something as of yet.
I have no idea, if e.g. "MMC"-card can be thought as "scsi-disk", and
thus be accessed as if via SCSI block driver interface.
If it can, then there are lots of examples of how to do that.
> Sincereley,
> Alexander Nassian
/Matti Aarnio
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