Hello Ulf and Adrian, This RFC patch is going to support enhanced strobe function for emmc version 5.1+ introduced by JEDEC recently. Firstly，from the former discussion of sdhci, I write these code inspired by Adrian's patch[0] for variant drivers to overwrite the callback in order not to add new callback into sdhci. And enchanced strobe is a optional function, so we add a new cap* for drivers to decide whether to use it. 1. History When introduing hs400 mode, JEDEC asks controllers to use data strobe line to latch the data from emmc devives. But for cmd-reponse, not mentioned yet. Since emmc version 5.1 published, JEDEC adds enhanced strobe function to deal with cmd-response the same way as dara-read. This feature is optional. 2. Current situation I can't find a upstreamed controller claimed to support it, as well as the mmc stack. But my "arasan,sdhci-5.1" actially supports this function. So I decide to work for this part. 3. About the code 1)This patchset is taken from Yi Sun's patch[1], but after reviewing the details and applying to test, I find some problems. We ask devices to switch to enhanced strobe mode, but we don't notify drivers to enable enhanced strobe mode. And we can't force controller to use enhanced strobe even if devices claims to support it. So I rework most of the code and take over the ownership from Yi Sun(If any objections here, please let know). 2)By looking into the SDHCI spec, I find there isn't any registers to enable the enhanced strobe function. But from my "arasan,sdhci-5.1" databook, it describes a register called VENDOR_REGISTER(0x78) to trigger this mode. So I guess other sdhci variant drivers may also need s vendor specific register to deal with it. 4. Howto If we are sure that our controller supports enhanced strobe mode, just add cap-enhanced-strobe in DT. Once emmc devices claims to support this mode, we enable it automatically. Of course, other sdhci*/non-sdhci drivers should implement/overwrite the prepare_enhanced_strobe by themselves. I believe all of the platforms which need to support this mode should do some basic preparation for their controllers. Reference: [0]: https://patchwork.kernel.org/patch/8262231/ [1]: https://patchwork.kernel.org/patch/6545421/ Shawn Lin (4): mmc: core: add cap-enhanced-strobe support mmc: core: implement enhanced strobe support mmc: sdhci: implement enhanced strobe callback mmc: sdhci-of-arasan: overwrite enhanced strobe callback Documentation/devicetree/bindings/mmc/mmc.txt | 1 + drivers/mmc/core/host.c | 2 + drivers/mmc/core/mmc.c | 54 ++++++++++++++++++++++++++- drivers/mmc/host/sdhci-of-arasan.c | 20 ++++++++++ drivers/mmc/host/sdhci.c | 11 ++++++ include/linux/mmc/card.h | 1 + include/linux/mmc/host.h | 8 ++++ include/linux/mmc/mmc.h | 2 + 8 files changed, 98 insertions(+), 1 deletion(-) -- 2.3.7 -- 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
