getting configuration info into a driver at load-time

getting configuration info into a driver at load-time

[Sebastian Kuzminsky]

Hi folks, i'm looking for a way to pass structured configuration 
information to a device driver at load-time.

I'm working on a device driver for a family of FPGA cards for motion 
control of industrial robots and computer-controlled machine tools.  The 
driver loads the FPGA firmware with request_firmware() and sends it to 
the FPGA.

Once the FPGA is up and running, the user needs to configure the 
firmware specifically for their machine, by telling the firmware things 
like "my machine has two stepper motors and three servo motors, and the 
second servo motor has an encoder with an index channel".  The details 
of the information being relayed isnt important, the key thing is that 
it's like a struct containing a couple of arrays of different kinds 
structs, something like this:

     struct config {

         struct {
             bool enabled;
             bool index_enabled;
             bool index_mask_enabled;
         } encoder_config[];

         struct {
             bool enabled;
         } pwmgen_config[];

         struct {
             bool enabled;
             uint width;
         } stepgen_config[];

         char *firmware;

         bool enable_raw;

     } board_config;


Each board that the driver finds should get its own "board_config".

I thought about exposing this config structure in /sys or /proc (in a 
per-board directory), and let the user poke in the config values after 
the driver has loaded, but I'd really prefer to make the information 
available at load-time.

Currently the driver has a module param array of char*, with each 
board's configuration encoded into an ascii string which gets decoded 
"by hand" in the driver.  Pretty grotty.

Is there some easier/cleaner way to do this?

-- 
Sebastian Kuzminsky
what i like best about 12648430 is the coffee

Re: getting configuration info into a driver at load-time

[Alan Cox]

> I thought about exposing this config structure in /sys or /proc (in a 
> per-board directory), and let the user poke in the config values after 
> the driver has loaded, but I'd really prefer to make the information 
> available at load-time.

Various drivers do load it after load time (and for one that allows you
to change the configuration without a restart which is usually a good
thing). In some cases driver that need a configuration to do sane things
fails other I/O with an error like EIO until a configuration is
established via ioctl or sysfs or similar.
 
> Currently the driver has a module param array of char*, with each 
> board's configuration encoded into an ascii string which gets decoded 
> "by hand" in the driver.  Pretty grotty.
> 
> Is there some easier/cleaner way to do this?

You can always request_firmware() the tables... bit hackish but works

Alan

Re: getting configuration info into a driver at load-time

[Kay Sievers]

On Tue, Oct 28, 2008 at 00:07, Sebastian Kuzminsky <seb@highlab.com> wrote:
> Hi folks, i'm looking for a way to pass structured configuration information
> to a device driver at load-time.
>
> I'm working on a device driver for a family of FPGA cards for motion control
> of industrial robots and computer-controlled machine tools.  The driver
> loads the FPGA firmware with request_firmware() and sends it to the FPGA.
>
> Once the FPGA is up and running, the user needs to configure the firmware
> specifically for their machine, by telling the firmware things like "my
> machine has two stepper motors and three servo motors, and the second servo
> motor has an encoder with an index channel".  The details of the information
> being relayed isnt important, the key thing is that it's like a struct
> containing a couple of arrays of different kinds structs, something like
> this:
>
>    struct config {
>
>        struct {
>            bool enabled;
>            bool index_enabled;
>            bool index_mask_enabled;
>        } encoder_config[];
>
>        struct {
>            bool enabled;
>        } pwmgen_config[];
>
>        struct {
>            bool enabled;
>            uint width;
>        } stepgen_config[];
>
>        char *firmware;
>
>        bool enable_raw;
>
>    } board_config;
>
>
> Each board that the driver finds should get its own "board_config".
>
> I thought about exposing this config structure in /sys or /proc (in a
> per-board directory), and let the user poke in the config values after the
> driver has loaded, but I'd really prefer to make the information available
> at load-time.
>
> Currently the driver has a module param array of char*, with each board's
> configuration encoded into an ascii string which gets decoded "by hand" in
> the driver.  Pretty grotty.
>
> Is there some easier/cleaner way to do this?

Maybe configfs?

Kay