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Date: Tue, 17 Apr 2007 08:15:54 -0700 From: Philip Langdale <philipl@...rt.org> To: Madhusudhan c <cr.madhusudhan@...il.com> CC: linux-kernel@...r.kernel.org Subject: Re: MMCv4 support (8-bit support missing) 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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