From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754458AbXDQPQK (ORCPT ); Tue, 17 Apr 2007 11:16:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754460AbXDQPQK (ORCPT ); Tue, 17 Apr 2007 11:16:10 -0400 Received: from usul.saidi.cx ([204.11.33.34]:59804 "EHLO usul.overt.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754458AbXDQPQI (ORCPT ); Tue, 17 Apr 2007 11:16:08 -0400 Message-ID: <4624E4AA.8050408@overt.org> Date: Tue, 17 Apr 2007 08:15:54 -0700 From: Philip Langdale User-Agent: Thunderbird 1.5.0.10 (X11/20070221) MIME-Version: 1.0 To: Madhusudhan c CC: linux-kernel@vger.kernel.org References: In-Reply-To: X-Enigmail-Version: 0.93.1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-I-Got-Here: Yes X-I-Got-Here: Yes3 Subject: Re: MMCv4 support (8-bit support missing) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Madhusudhan c wrote: > Hi Pierre/philip, > > This is regarding the MMCv4 support that came in as part of the MMC > core of 2.6.20 linux kernel version. > > The high speed MMC cards can support 4-bit/8-bit transfers. The 8-bit > support seems to be missing from the MMCv4 support implemented by > Philip Langdale . > To support 8-bit transfers the core needs to implement "bus testing > procedure". This requires support for CMD19 and CMD14. > > Why is the support for bus testing procedure msiing from the MMCv4 support? Because we have not seen any 8-bit hardware - let alone any 8-bit hardware which we know how to drive. It is unclear how necessary the bus testing sequence is, but the main reason why it's not there is that I could never get it to work on the sdhci controller I use for testing. Due to how the CRC is handled for these commands, the controller gets confused, reports failure, and doesn't provide the returned data - making the test impossible. If you have found an 8-bit controller that we can support, we'd love to know about it! --phil