Samuel Thibault, on mar. 14 mars 2017 01:47:01 +0100, wrote:

Greg KH, on mar. 14 mars 2017 06:14:04 +0800, wrote:

quoted

On Mon, Mar 13, 2017 at 10:05:51PM +0000, okash.khawaja@gmail.com wrote:

quoted

This patchset introduces a TTY-based way for the synths to communicate
with devices as an alternate for direct serial comms used by the synths
at the moment. It then migrates some of the synths to the TTY-based
comms. Synths migrated in this patchset are dummy, acntsa, bns and
txprt.

What about using the serbus code that is now in the tree?  That should
make this a lot easier than your patchset from what I can see.

Mmm... AIUI from reading tty_port_register_device_attr, one
would have to have registered a speakup serdev device driver
*before* tty_port_register_device_attr gets called, so that
serdev_tty_port_register matches the driver in the loop of
of_serdev_register_devices, and no TTY cdev is created?

That would mean that speakup can not be loaded as a module after ttyS0
initialization, that won't fly for our use needs. The line discipline
mechanism allows us to attach ourself to an existing tty.  Could we
imagine a tty_port function which removes the cdev and tries to register
the tty port again to serdev?

What we basically need to be able to say on speakup module load is
e.g. "I'm now attaching a device to ttyS0, use this serdev_device_ops to
discuss with it".

That for_each_available_child_of_node loop is really way more complex
than what we need.  And what's more, it's not working without CONFIG_OF
(!)

It would really make sense to me to have a

serdev_device *tty_port_register_serdev_device(tty, device)

which unregisters the character device of the tty, and creates instead a
controler with the given device plugged to it. Really much like a line
discipline, but way simpler :)

The issue that remains is the "tty" part: we'd need there the tty_port,
the parent device, the tty driver, the idx. All we know when we load
speakup is "ttyS0". That's where going through the cdev to attach a line
discipline was simpler :)

Samuel