two drivers for the same piece of hardware?

[Clark Kent]

Hi guys,

I am wondering what happens if there are two drivers installed that are both compatable with the same piece of hardware. I am fairly new to linux and I've been trying to figure out how things work. As I understand it, the device driver registers the device numbers (major and minor) it wants to use. I assume that udev creates the corresponding device file in /dev only if the hardware is physically connected to my box. My question is what happens when there are two drivers that are capable of controlling the same piece of hardware. Do they get different device numbers and different device files? If this were the case then I guess the user program that requires the device would choose what device file it wants to use? But, as I understand it, many of the device numbers are standardized - so two device drivers may try to register the same major node if they want to control the same piece of hardware - so how is it decided what driver gets it? Also, I am wondering if there is a tool in linux that will tell me all the drivers installed and what devices they are support. Assuming it is possible to have more than one driver installed for the same piece of hardware, is there a way to specify the default driver to be used? Could somebody please set me straight.

Thanks for your help and time!

[kabage]

Yes there can be many drivers but usually only one can be using the hardware at a given time

exampe arts vs alsa just from my experience arts can interrupt alsa and play over but
nothing can interrupt arts if it has control of the sound card. So I would say most of the time
it is first come first serve with a few exceptions on sound.


technically there is only one device for each hardware in /dev set up by udev
though there could be multiple links to the device like /dev/cdrom pointing to /dev/hdc

Most applications use one driver , again sound you might have a choice like arts or alsa or oss
so that is application dependent on if you have a choice.

Most applications other than sound don't really,
video cards there are linux vs commercial drivers but that is setup in xorg conf on which one you want
to use, I mean you can change the driver once your gui is started you have to shutdown and restart to
engage the new or alternate driver.


I'm sorry if I am making it worse, to summarize yes many drivers, typically first come first serve as
to which driver is engaged and only ONE device set up by udev or whatever per piece of hardware.

Edit: Regarding devices

lspci (in package pciutils)
or lshw are real good about listing devices
but I can think of nothing off hand that will show you what driver you should use. there is few things that will show you what
driver they are using after the fact, by the time you learn your hardware and which driver it uses will you get picture ,
you become very intimate with your hardware.

if you set yourself up like a liveCD there are a couple of good tools I can't remember off hand but basically will
set up all your devices on the fly, but the overhead is quite a bit. But it is more difficult to make a liveCD then just
download PCLinuxOs or Knoppix which never cease to amaze me how well they can identify and load drivers on the
fly.
_________________
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[Clark Kent]

Thanks for the response!
The lshw program you recomended works well, thanks! I still have a few questions.

If both drivers, arts and alsa, are controlling the sound card, and if there is only one special device file for the sound card, does the kernel let them both register the same major node (i think it's 14 for sound)?

In general, does the kernel allow more than one driver to register the same major node?

As I understand it, each device number is associated with its own set of functions (open, read, etc). There is a mechanism to have these functions point to the specific functions in the driver that implement them. So it seems impossible that two drivers can register the same device number - since they both need to have the "standard functions" (open,read,etc) point to their implementations. So I am still confused how two drivers can control the same hardware.

what do you mean by first come first serve? to register the device number? to execute the function being called by an application?

I am interested in any tool that will show me the names of the drivers that are installed after the fact! Could you let me know what tools those are?

[kabage]

lshw -X

should show you the drivers although, a little maybe cryptic