From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755874Ab0DBRV2 (ORCPT ); Fri, 2 Apr 2010 13:21:28 -0400 Received: from 82-117-125-11.tcdsl.calypso.net ([82.117.125.11]:48923 "EHLO smtp.ossman.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755299Ab0DBRVW (ORCPT ); Fri, 2 Apr 2010 13:21:22 -0400 X-Greylist: delayed 317 seconds by postgrey-1.27 at vger.kernel.org; Fri, 02 Apr 2010 13:21:22 EDT Date: Fri, 2 Apr 2010 19:16:00 +0200 From: Pierre Ossman To: "Ramesh.R" Cc: linux-kernel@vger.kernel.org, srini@arasan.com, ramesh@arasan.com Subject: Re: 64 bit Descriptors in ADMA of Linux SDHost controller driver. Message-ID: <20100402191600.19af3ffc@mjolnir.ossman.eu> In-Reply-To: References: X-Mailer: Claws Mail 3.7.5 (GTK+ 2.18.7; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; protocol="application/pgp-signature"; boundary="=_freyr.ossman.eu-11662-1270228563-0001-2" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a MIME-formatted message. If you see this text it means that your E-mail software does not support MIME-formatted messages. --=_freyr.ossman.eu-11662-1270228563-0001-2 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 1 Apr 2010 14:46:14 -0700 "Ramesh.R" wrote: > Hi Pierre Ossman, >=20 > When we go though the Linux Standard SD Host controller driver(Using the > Kernel 2.6.33), we saw only the 32 bit Descriptors implemented in it. >=20 > We confirmed this status for 32 bit and 64 bit processors. >=20 > Are these observations correct. Please clarify us. >=20 Quite. The hardware I had at my disposal only supported 32-bit descriptors and I didn't want to write code that I had no way of testing. > Also how the 64 bit machines will process the data, if the Descriptors are > implemented with 32 bit. If they are using the 32 bit and don't care about > the MSB 32 bits, then there is no major difference in performance wise, > whether it is 32 or 64 bit processors. Please correct me if my understand= ing > is wrong. The only performance impact that might occur is if you try to transfer to/from an address above 4 GiB, at which point you need a bounce buffer and an extra memory copy. (I believe the kernel does this by default if the driver doesn't explicitly say that it is 64-bit compatible) >=20 > Also please point us, if we need to use 64 bit addressing for DMA > descriptors is there any way with the current SD host controller or not. >=20 It's been quite some time since I looked at the driver, but I seem to recall that adding 64-bit support is not a particularly difficult task. As long as you have hardware for testing then it is something that you should be able to sort out with less than a week of work. Rgds --=20 -- Pierre Ossman WARNING: This correspondence is being monitored by FRA, a Swedish intelligence agency. Make sure your server uses encryption for SMTP traffic and consider using PGP for end-to-end encryption. --=_freyr.ossman.eu-11662-1270228563-0001-2 Content-Type: application/pgp-signature; name="signature.asc" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.13 (GNU/Linux) iEYEARECAAYFAku2JlIACgkQ7b8eESbyJLgFZQCghFqvWYO+5C47Qp3XyF2EDIHD kfMAniFlo/ObXC+50v1grmZIEUqFzDC8 =d5dm -----END PGP SIGNATURE----- --=_freyr.ossman.eu-11662-1270228563-0001-2--