Philip Langdale wrote: > On Thu, 8 Oct 2009 20:38:26 +0200 > Pierre Ossman <pierre@xxxxxxxxx> wrote: > >>> In practice, I expect that the timings are close enough that this >>> will work anyway, but I think the situation is analogous to HS-MMC >>> vs HS-SD. There the timings are slightly different and you felt it >>> was enough to justify a separate host cap for each one. >>> >> It's difficult to say without seeing the spec. But if things are not >> backwards compatible, then we should probably add either a new timing >> mode, or a new bus mode (where we have open drain and push pull >> today). >> >>> In fact, thinking about it in those terms, it suggests we need to >>> retroactively introduce a reduced-voltage MMC host flag too, just in >>> case SDHCI 3.0 controllers barf on those cards... >>> >> Maybe. Again, it's difficult to say without seeing the specifics of >> the new specification. > > Make sense. So, I guess the question is do we assume the best case (in > which case there is no additional work to do - the code that is now > in allows low voltage SDIO cards to try and run) or the worst case and > add pre-emptive mode flags? > > David, you've actually seen the new spec right? What's your opinion? In the 3.00 spec, OCR bit 24 is S18R (Signalling 1.8V request). This is outside of the VDD region (bits 0:23). So I think we can support non standard DS/HS (Default Speed/High Speed) cards that report 1.8V operation (in the VDD region) and new UHS-I (Ultra High Speed phase I) cards without any confusion. On a UHS-I capable controller, the software would send ACMD41 with S18R set and see if the card responses with it set. If so, it tells the card to switch to 1.8V signalling (CMD11) and tells the controller to switch to 1.8V signalling and SDR12 mode. The controller still supplies 3.3V to the card even after the switch. Later on the host software will query the card to find out what UHS-I modes are supported and switch card and controller to a faster mode (if possible). David -- David Vrabel, Senior Software Engineer, Drivers CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562 Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/ Member of the CSR plc group of companies. CSR plc registered in England and Wales, registered number 4187346, registered office Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
