libftdi Archives

Subject: Re: Claiming devices has no effect under Linux

From: Thomas Klose <thomas.klose@xxxxxxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Wed, 06 Oct 2010 22:55:10 +0200
Am Mittwoch, den 06.10.2010, 22:27 +0200 schrieb Uwe Bonnes: 
> >>>>> "Thomas" == Thomas Klose <thomas.klose@xxxxxxxxxxxxx> writes:
>     Thomas> Am Mittwoch, den 06.10.2010, 15:39 -0400 schrieb DJ Delorie:
>     >> > If the device has a VID/PID which is associated with a kernel
>     >> module I > would expect that module to be loaded. If a device is not
>     >> intended to be > used with sio it *must* use another VID/PID. This is
>     >> the whole idea > behind the VID/PID system.
>     >> 
>     >> What about a device which *is* intended to be used by sio, but
>     >> *sometimes* you want to bit-bang it instead?
>     >> 
>     >> In my case, I use the FT232R chips as usb-to-serial ports for my
>     >> MCUs, but to *program* the MCU, I have to fiddle with the cbus pins
>     >> too.  For that task, I need to load libftdi.  For normal
>     >> communications I just use /dev/ttyUSB* via sio.
>     Thomas> I do not see the problem. In this case you could detach sio with
>     Thomas> modprobe, rmmod, usb_detach_kernel_driver(), or whatever in your
>     Thomas> *application*. I am just saying, detaching driver modules as
>     Thomas> default behavior of a *library* seems surprising to me, because
>     Thomas> it generalizes this not very beautiful, yet necessary and valid
>     Thomas> approach.
> But rmmod requires being root, while our concept only requires access to the
> device.
But usb_detach_kernel_driver() doesn't. So no harm done.

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