From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Farnsworth Subject: Re: [PATCH] saa7134: Add pm_qos_request to fix video corruption Date: Mon, 29 Oct 2012 16:03:04 +0000 Message-ID: <2614655.PC7gBWDYxH@f17simon> References: <1350906611-17498-1-git-send-email-simon.farnsworth@onelan.co.uk> <13391942.y8AEurCsVE@f17simon> <20121029134445.1f58657e@infradead.org> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart1879889.QENECiXHnW"; micalg="pgp-sha1"; protocol="application/pgp-signature" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20121029134445.1f58657e@infradead.org> Sender: linux-media-owner@vger.kernel.org To: Mauro Carvalho Chehab Cc: Andy Walls , linux-media@vger.kernel.org, linux-pm@vger.kernel.org List-Id: linux-pm@vger.kernel.org --nextPart1879889.QENECiXHnW Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" On Monday 29 October 2012 13:44:45 Mauro Carvalho Chehab wrote: > Thanks for digging into it and getting more data. Do you know if this change > it also needed with USB devices that do DMA (isoc and/or bulk)? Or the USB > core already handles that? > I'm not a huge expert - the linux-pm list (cc'd) will have people around who know more. If I've understood correctly, though, the USB core should take care of pm_qos requests if they're needed for the hardware; remember that if the HCD has enough buffering, there's no need for a pm_qos request. It's only needed for devices like the SAA7134 where the buffer is small (1K split into pieces) compared to the sample data rate (27 megabytes/second raw video). For the benefit of the linux-pm list; this all starts with me providing a patch to have the saa7134 driver request reduced cpu_dma_latency when streaming, as I've seen buffer exhaustion. We've got far enough to know that the value I chose was wrong for the saa7134, but Mauro also wants guidance on whether USB devices (not host controllers) also need to request reduced latency. -- Simon Farnsworth Software Engineer ONELAN Ltd http://www.onelan.com --nextPart1879889.QENECiXHnW Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQEcBAABAgAGBQJQjqi7AAoJEIKsye9/dtRWaZgH/i/Tgt8cDMdxqgijvQClkqcE O5LBJhuPVg/cOA5JoqhwUNBHo2RdNzvHP4SsmpJd1eXZJzMONAJK9+gGKXqgflHc a+Ib3ow6CYZ83QwFhlOp1llcPtft65uEBNZ8BL6YU1wy96TFo/k+Ba/jGfnTygJO 0bLiLblZKuaa3pMqdSEUD5i/0JRcHeY7LQK0tL+kGtOQnYRJrDuCNGKqfNeCQGDW HbovJ6zenh7z3ZZf2spKG5k2ZDGDdiIh6XRG094TyhfaSl6Y4e9POXwXXZ9g2i6e QeAokiIudhOpky5u0QN9+PuyMfA10rbtA3YTrCpSf4nQ8drcACv9kKLCEezXZKA= =UVli -----END PGP SIGNATURE----- --nextPart1879889.QENECiXHnW--