Johannes Erdfelt wrote:
>
> On Mon, May 29, 2000, David Brownell <[EMAIL PROTECTED]> wrote:
> > Re control queuing, I think that's likely the wrong model.
> >
> > Scenario: driver1 sees some state, issues a control request
> > based on it. Concurrently, driver2 does the same. One of
> > them "wins" the race, and the state when its request completes
> > makes the other driver's request into something undesired (an
> > error, corrupts state, etc).
>
> That is a problem, but I think 2 drivers (or driver and process) won't
> be controlling the same part of a device.
no, but they might be controlling two seperate parts of the same device by
using the same control port... and the same status information.(even if only
one of the parts can influence that status, you still have the race...)
> Take the HID driver. It sets up some simple stuff at the beginning
> (configuration, alternate setting, hid specific stuff, etc) and the only
> does HID control messages to turn on leds, set hid specific parametes,
> etc.
Say an ADSL modem driver, it sets up the modem and does the management from
user or kernel space.
> Then we have some userspace client which does a control transfer to
> request some descriptors or something (string, device, etc).
And a seperate part that does the real traffic transport on a certain
endpoint. It needs the status of the ADSL modem (UP or DOWN). Actually, I
think it doesn't really need it but it is useless to send huge amounts of data
over the USB bus that will be dropped anyway...
I can probably avoid that in this driver, but it might not always be the case.
(Currently the two parts are still united, this avoids the problem for me...)
J.
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