On Wed, Feb 24, 2021 at 01:13:39PM -0500, Michael G. Katzmann wrote:

On 2/24/21 12:04 PM, Johan Hovold wrote:

quoted

Perhaps you can even figure out how to poll for an empty TX FIFO from
it, unless Charles is able to provide some details on that separate
matter?

I presume from the code below, that when the device is closed, all
data waiting to send is clobbered (if so, so the problem is the driver
and not the device)

I would have thought that the driver should drain the buffers. I can
see that this might be a problem if there is flow control (it may
never drain) but the current method seems pretty brutal.

We do; the code below isn't called until after we've waited for the
buffers to drain (driver buffers + device FIFO).

I'll provide a patch so that you can extend the timeout for draining the
driver buffers (defaults to 30 s), but the main problem is that we don't
know how to query the PL2303 FIFO fill level.

119 void usb_serial_generic_close(struct usb_serial_port *port)
120 {
121         unsigned long flags;
122         int i;
123
124         if (port->bulk_out_size) {
125                 for (i = 0; i < ARRAY_SIZE(port->write_urbs); ++i)
126                         usb_kill_urb(port->write_urbs[i]);
127
128                 spin_lock_irqsave(&port->lock, flags);
129                 kfifo_reset_out(&port->write_fifo);
130                 spin_unlock_irqrestore(&port->lock, flags);
131         }
132         if (port->bulk_in_size) {
133                 for (i = 0; i < ARRAY_SIZE(port->read_urbs); ++i)
134                         usb_kill_urb(port->read_urbs[i]);
135         }
136 }

Johan