linux-kernel - Re: [PATCH] firewire: adopt read cycle timer ABI from raw1394

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Date:	Sat, 29 Sep 2007 11:01:51 +0200 (CEST)
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Kristian Høgsberg <krh@...hat.com>,
	Pieter Palmers <pieterp@...w.be>
cc:	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firewire: adopt read cycle timer ABI from raw1394

> This duplicates the read cycle timer feature of raw1394 (added in Linux
> 2.6.21) in firewire-core's userspace ABI.

Kristian and Pieter, does this simple duplication of the ioctl make
sense on its own?  AFAIU rawiso's iso packet buffers look different from
fw-cdevs's. It seems to me as if rawiso always put the cycle into a user
buffer for each iso packet received...

raw1394.h::struct raw1394_iso_packet_info {
	__u32 offset;
	__u16 len;
	__u16 cycle;   /* recv only */
	__u8  channel; /* recv only */
	__u8  tag;
	__u8  sy;
};

raw1394.c::raw1394_iso_recv_packets()

	/* copy the packet_infos out */
	for (i = 0; i < upackets.n_packets; i++) {
		if (__copy_to_user(&upackets.infos[i],
				   &fi->iso_handle->infos[packet],
				   sizeof(struct raw1394_iso_packet_info)))
			return -EFAULT;

		packet = (packet + 1) % fi->iso_handle->buf_packets;
	}

...while the Juju ABI returns the cycle only for those packets whose
fw_cdev_iso_packet.control had the FW_CDEV_ISO_INTERRUPT flag set.
The cycle is then written out in the fw_cdev_event_iso_interrupt event
which happens when this particular packet was received.  Right?

Pieter, do applications like yours need the cycle counter only for a few
predetermined packets or for each and every packet?
-- 
Stefan Richter
-=====-=-=== =--= ===-=
http://arcgraph.de/sr/

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