netdev - Re: [Linux-zigbee-devel] [PATCH 1/6] mac802154: Immediately retry sending failed packets

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Message-ID: <20130403023821.GE28141@ws>
Date:	Tue, 2 Apr 2013 23:38:21 -0300
From:	Werner Almesberger <werner@...esberger.net>
To:	Alan Ott <alan@...nal11.us>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	linux-zigbee-devel <linux-zigbee-devel@...ts.sourceforge.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [Linux-zigbee-devel] [PATCH 1/6] mac802154: Immediately retry
 sending failed packets

Alan Ott wrote:
> 1. Most supported devices have only single packet output buffer, so
> blocking in the driver is the most straight-forward way to handle it.
> The alternative is to make each driver have a workqueue for xmit() (to
> lift the blocking out from atomic context). This makes each driver simpler.

It does make following the program flow a little easier, but
the difference isn't all that large if you think of it,
particularly if you have to wait not only for I/O to finish
but also for the device to send the packet.

The latter will usually be signaled by some form of interrupt,
so you're already in a situation where a callback to the higher
layers of the stack would be very natural.

> Maybe at some point this will be done. Right now we have a ton of
> pressing issues (in my opinion).

Agreed on having no shortage of nasty issues :-) And I'd like
to echo Dave's comment regarding netdev. Those ieee802154_dev
always struck me as peculiar, with flow control just being one
issue.

And things get worse when you have a complex bus underneath
your driver. For example, my USB-using atusb driver (*) has to
do a great many things usbnet already does. And any other
USB-based WPAN driver would be more or less in the same boat.
Of course, one could reinvent that wheel as well and make a
usbwpan, but ... :)

(*) Sneak preview, still with a number of issues, not only style:
    https://github.com/wpwrak/ben-wpan-linux/blob/master/drivers/net/ieee802154/atusb.c

- Werner
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