Hi Ulf, 2016-12-13 16:52 GMT+09:00 Ulf Hansson <ulf.hansson@xxxxxxxxxx>: > [...] > >>>> + >>>> +Optional properties: >>>> +For eMMC configuration, supported speed modes are not indicated by the SDHCI >>>> +Capabilities Register. Instead, the following properties should be specified >>>> +if supported. See mmc.txt for details. >>>> +- mmc-ddr-1_8v >>>> +- mmc-ddr-1_2v >>>> +- mmc-hs200-1_8v >>>> +- mmc-hs200-1_2v >>>> +- mmc-hs400-1_8v >>>> +- mmc-hs400-1_2v >>> >>> There's now a property to override SDHCI capabilities register. Maybe >>> you should use that instead? I'll defer to Ulf. >>> >> >> I did not know this new property. >> >> So, now we have two ways to specify MMC speed mode capabilities >> by only touching DT. > > Let me clarify a bit. > > The point with the new bindings is to be able to override *broken* > SDHCI caps bits. So, not only related to the speed modes. Right. So my approach ([1] Add MMC mode flags directly) basically sounds OK. >> >> [1] Add MMC mode flags directly, like I did. >> [2] Use "sdhci-caps-mask" and "sdhci-caps" >> >> >> The problem for [2] is that eMMC capabilities >> do not perfectly correspond to the SDHCI capabilities register. >> >> >>>> +- mmc-hs400-1_8v >>>> +- mmc-hs400-1_2v >> >> If the driver sets SDHCI_QUIRK2_CAPS_BIT63_FOR_HS400, >> we can use the bit63 of caps for specifying HS400. >> >> But, this is not defined in the SDHCI standard. >> #define SDHCI_SUPPORT_HS400 0x80000000 /* Non-standard */ >> >> >> >>>> +- mmc-ddr-1_8v >> >> For High Speed DDR, perhaps we can imply MMC_CAP_1_8V_DDR >> from MMC_CAP_UHS_DDR50 (bit34 of caps) >> >> This is not supported in the current code, but >> if this is a good idea, I can send a patch. >> >> >>>> +- mmc-ddr-1_2v >> >> This does not have the corresponding bit, but >> 1.2V is not commonly used, so this is not a fatal problem. >> >> >> >> What I can do at most now, is to delete the >> Optional properties section entirely >> so users can choose [1] or [2] as they like. >> > > I think a better approach is to use the new sdhci-caps* bindings to > mask those caps that can't be trusted. And then use the generic mmc > bindings for speed modes instead. > > That should be a safer approach, right!? Right. But, if I know the caps register bits 63-32 are all zero, I need not explicitly specify sdhci-caps-mask, right? -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
