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

[Richard Clark <richardc@xxxxxxxxx>]

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.

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);
}

Thanks for any info.

--
Richard C


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