Re: [PATCH 14/16] USB: Add usbfs ioctl to get the frame number

On Fri, May 04, 2007 at 11:56:18AM -0400, Alan Stern wrote:
> From: Danny Budik <[email protected]>
> 
> This patch (as899) adds a new ioctl to usbfs: USBDEVFS_GETFRAMENUM.
> It allows user programs to obtain the current Start-Of-Frame number on
> a USB bus.
> 
> Note that the values returned by the get_frame method in the various
> host controller drivers are not consistent.  They should be adjusted
> so that they provide the actual frame number as it appears on the bus;
> that is, a number incrementing by one every millisecond, ranging from 0
> to 2047.  That will have to be done separately; it interacts with the
> start_frame values used for submitting Isochronous URBs.
> 
> Signed-off-by: Alan Stern <[email protected]>

As this value will be wrong, and will be out-of-date due to timing
issues going to userspace and back, I still don't see the use of adding
this to our kernel at this point in time.

People will only start using it, to then find out that it's really
broken, and then we have to support it forever in the future.  That
doesn't sound very fun :)

thanks,

greg k-h

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