On Sun, 28 Jan 2007, Oleg Verych wrote:
> On Sun, Jan 28, 2007 at 03:25:40PM -0500, Alan Stern wrote:
> > > What about to have ID-config-interface table? This will show, what
> > > "drivers" are, and will give full usb-device setup capability, without
> > > assumptions and userspace involving, as it should be.
> >
> > I don't understand. Please provide more details. Exactly what
> > information would you like to see in this "ID-config-interface table"?
> >
>
> {{vID, dID}, #working_configuration, #woring_interface }, obviously.
>
> To be honest, i can't understand, why you don't understand this.
Part of the problem is that I find it difficult to follow your English.
This isn't meant as a complaint! Your English is infinitely better than
my Czech. But sometimes it is hard to grasp your intention.
Also you sometimes leave out or skip over important aspects of the
reasoning. Like here, for instance. It may have been obvious to you why
you wanted to add #working_configuration and #working_interface values to
the ID table, but it wasn't -- and still isn't -- entirely clear to me
why you want them.
> I
> think to provide all configuration path, without jumping thru air
> isn't such a bad idea.
Well, consider what you have just proposed. For example, let's say we
have this entry in an ID table:
vID=0x1234, dID=0x5678, #working_config=3, #working_interface=5.
Such an entry matches only when all its conditions are met, i.e., when the
vendor ID is 0x1234, the device ID is 0x5678, the config value is 3, and
interface number is 5.
What advantage does this have over the existing situation? Using the
current code, a driver could specify an ID table entry saying:
vID=0x1234, dId=0x5678
Then the driver itself could easily return -ENODEV if the config value
wasn't 3 or the interface number wasn't 5. So the new fields in the table
have no real point.
Furthermore, USB interface drivers hardly ever care what the config
value or interface number is. All they care about are the interface's or
device's class, subclass, and protocol (or the device's vendor and product
IDs).
Cases where the driver does care about the config value or interface
number occur so rarely that I don't see any point in adding them to the
tables. It would bloat the tables, and it wouldn't add any new
functionality.
Alan Stern
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