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Writing a Linux Device Driver on Company Time?
DriverSubversion asks: "Excuse the anonymity: I'm covering my back and that of my company. My company makes some USB and PCI peripherals, currently only supported under Windows. Several of us have pointed out that there is a large cross-over between the people who buy these things and the people who run linux - and thus it's in the company's best interest to develop device drivers for Linux,as well as Windows. Now while our boss is kind of convinced that this might sell some more units, he understandably wants to know how much it will cost to write and maintain the drivers... and where better to ask than here? So has anyone else gone though this? On scale of 1-10, how hard is it, (1 being 'extremely easy, 2 programmers could do it' and 10 is 'a team of no less than 20 programmers, lawyers and salesmen'). Keep in mind that our intent is to keep the code up-to-date, GPL-compliant and in at least some major distributions."
If you can convince the PHBs to release it under the GPL, then you don't have to spend time or money maintaining it. One of the kernel janitors will probably port it to new kernels.
Take a look at many of the USB serial drivers; tiny drivers, very clean. The USB storage drivers, same thing (assed-up hardware is the reason for complexity in those drivers).
Writing a device driver for Linux is no more difficult than writing a device driver for Win32. You're in Ring 0 (for ia32) for both, so a poor driver can cause the system to come down. My suggestion would be to take a look at what you've written for win32, estimate how much of that you can keep, and write the linux kernel abstraction layer code.
If you've written the driver correctly it shouldn't be a very large task at all, I would imagine.
The easiest way to get a Linux driver would be to give find an interested developer, give them a free device and detailed documentation, and answer any questions they have. If you're working on a tight budget, this might be the best option.
There are lots of people who attempt to write a driver for a device, but fail only because the manufacturer won't give them information. IMHO, this doesn't make much sense - if someone wants to help you out for free, why would you stop them?
You don't want the drivers in distros -- you want them in
Linus' kernel. Don't worry about liason with distro vendors.
Worry about liason with vger.
Since understanding the device, finding its quirks, and
designing protocol is the overwhelming bulk of the work
of writing a device driver, a reasonable rule of thumb is
that adding another platform will entail an additional
10-20% in manpower. Since the gap between a WinXP
driver and a Linux driver is relatively large, the high-end
of the scale is a closer approximation: Take the
development time for the Windows driver and divide by 5.
Now for maintenance, the new platform cost is much higher,
because each platform has its quirks, etc. You do get to
amortize some stuff over the platforms (no need to
diagnose protocol bugs twice, etc.), but it doesn't count
for a whole lot, so I would estimate that adding a new
platform will entail 80-90% again as much in maintenance
costs.
However, for an open source driver, you will quickly find
(if your hardware is at all useful) that the chore of forward-
porting maintenance as the kernel develops will be largely
assumed by the user community, so give any open-source
platform a -25% maintenance cost tick, at least.
Customer support issues are an entirely different ballgame,
and depend so much on your audience that I won't venture
even a guess -- keep in mind that customer support for
a smaller community typically is less work than is a similar
level of support for a larger community -- and Linux
users are accoustomed to self-support and community-support.
win_cost = win_dev + win_maint + win_support
lin_cost = lin_dev + lin_maint + lin_support
lin_dev = win_dev * 0.2
lin_maint = win_maint * 0.6
lin_support = win_support * k
Fill in k.
-I like my women like I like my tea: green-
If you can convince the PHBs to release it under the GPL, then you don't have to spend time or money maintaining it. One of the kernel janitors will probably port it to new kernels.
Maybe, but I hope you don't give hardware companies those kinds of ideas.
A hardware company really should, ideally, maintain the drivers for their own products AND work with the kernel janitors or maintainers to keep an up to date copy in the Linux kernel sources.
The kernel guys do great with most of the drivers they write, but it seems like it's best for the hardware company to do it 1) out of courtesy, to prevent others from having to maintain drivers that make the company money, and 2) for quality control -- the community might not know how to get the most out of the device.
I have done some driver work, build and debuging and linux is a driver writers dream compared to windows. I would estimate that a linux driver will consume about 50% as much time as a windows drive writing either from scratch. I reality, you may have a lot or reusable code from the windows drivers so you could be looking at less. Also do take the advice of other posts and get the basic driver out ASAP, and allow the OS community help out on the rest.
Maybe, but what kind of performance cost are you facing? And how are any 3rd parties meant to maintain the driver then?
Does your company support OS X as well? Just remember that Mac customers tend to have the extra discretionary income to purchase all sorts of Firewire and USB goodies... Be a sport and advocate for a multi-polar OS environment, Win32, OS X, and Linux... I relinquish control of the soapbox...
"Right now, somewhere in this world, Scott Baio is plowing a woman he doesn't love," - Peter Griffin, *Family Guy*