Extending sys/dev/mii

[Oleksandr Tymoshenko]

On 2012-01-20, at 8:13 PM, Oleksandr Tymoshenko wrote:

> On 20/01/2012 5:43 PM, Warner Losh wrote:
>> 
>> On Jan 20, 2012, at 5:08 PM, Stefan Bethke wrote:
>>> The second problem is that there's currently no way to express a dependency between two devices other than a parent-child relationship.   I would be interested to learn why this appears to be so uncommon that I could not find any discussion of such a feature.  Has it really never before come up?
>> 
>> Sure there is: you can do it by name.  I wrote a driver that attached to the ISA bus, but also needed to talk to the ppbus that was attached to the printer.  My solution was to have a post-attach name-lookup so that it could then call methods on the other driver's device_t.  I wonder why we can't do that here?
> 
>    I've been thinking about it recently in regard to GPIO subsystem.
> And the same issue appeared during OMAP code import: there are at least
> two subsystems that are used by the rest of the drivers. Ben's suggested
> following solution: define kobj interface if_SUBSYTEM.m and then
> provide API call in form:
> 
>    int omap_prcm_clk_enable(clk_ident_t clk)
>    {
>        device_t prcm_dev;
> 
>        prcm_dev = devclass_get_device(devclass_find("omap_prcm"), 0);
>        if (prcm_dev == NULL) {
>            printf("Error: failed to get the PRCM device\n");
>            return (EINVAL);
>        }
> 
>        return OMAP_PRCM_CLK_ENABLE(prcm_dev, clk);
>    }
> 
> So it might make sense to create some kind of upper-level API for
> defining this kind of subsystems' APIs since every implementation
> would duplicate a lot of code: look for instance of specific
> devclass, check if it exists. Not sure how to do it at the moment
> though.


I tinkered a little bit with this idea and here is what I've come up with so far:

http://people.freebsd.org/~gonzo/patches/horizontal-api.diff

this patch adds one more available declaration to .m files: APIMETHOD
In addition to usual kobj method declaration one more function is generated.
This function gets first device in devclass with the same name as declared
interface and uses it as object for respective method call. 

Also if there is at least one APIMETHOD in interface one more function called 
XXXX_available() is generated. It returns 1 if there is device of required devclass.

Usage example:
       int maxpin;

       printf("GPIO available: %d\n", gpio_available());
       if (gpio_available()) {
           gpio_pin_max(&maxpin);
           printf("GPIO pins: %d\n", maxpin);
        }

Possible improvements: instead of using devclass for identifying kobj, 
create way for device to explicitly register/deregister as an API "provider". 


Comments, ideas?