Re: usblp : Seiko/Epson Printer M129C - poll/select always POLLIN

On Wed, Dec 19, 2007 at 06:00:26PM -0800, Richard Clark wrote:
> I am using an Epson BA-T500 controller board that identifies itself the
> same as the Seiko/Epson Printer M129C that was recently added to the
> kernel.
> 
> In the past I had used my own driver created off of usb-skeleton.c, and
> I did not bother with the bi-directional side.
> 
> Now that it's in the usblp.c driver, along with it's quirks, I am
> starting to make use of the inbound bulk endpoint for printer status.
> 
> My problem is that even if there is no data present, the URB request
> completes and usblp->rcomplete is flagged.  This is causing my
> poll/select call to always trigger even when there is no data.
> 
> Question - 1
> Is this action normal for class based usb printers ? ie, the URB request
> will complete and return even if there is no data.

What does the usb printer spec say about this?

> Question - 2
> I have solved my problem by changing the usblp_buld_read callback to
> check for data before flaging usblp->rcomplete, and if not, resubmitting
> the URB.  Is there any problem with doing as I have below ?  
> 
> static void usblp_bulk_read(struct urb *urb)
> {
>         struct usblp *usblp = urb->context;
> 
>         if (unlikely(!usblp || !usblp->dev || !usblp->used))
>                 return;
> 
>         if (unlikely(!usblp->present))
>                 goto unplug;
>         if (unlikely(urb->status))
>                 warn("usblp%d: nonzero read/write bulk status received:
> %d",
>                         usblp->minor, urb->status);
>         if (urb->actual_length)
>             usblp->rcomplete = 1;
>         else {
>             if (usb_submit_urb(usblp->readurb, GFP_ATOMIC) < 0)
>                 err("usblp%d: Error resubmitting read urb",
> usblp->minor);
>         }
> unplug:
>         wake_up_interruptible(&usblp->wait);
> }

Can you send this in diff format so we can see exactly what was changed?

thanks,

greg k-h

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