On Fri, Jul 27, 2018 at 11:05:55AM +0300, Aapo Vienamo wrote: > On Thu, 26 Jul 2018 15:05:55 +0200 > Stefan Agner <stefan@xxxxxxxx> wrote: > > > On 26.07.2018 14:19, Aapo Vienamo wrote: > > > Add a property to mark controllers which operate at a 1.8 V fixed I/O > > > voltage. > > > > > > This feature of the hardware needs to be signaled this way because it > > > cannot be probed at runtime or reliably derived from other properties. > > > > Is this really needed? Can we not use vqmmc to determine which voltage > > the controller runs on? > > > > There is already some precedence in the SDHCI core to determine which > > voltage levels are supported: > > https://lkml.org/lkml/2018/7/5/342 > > This property is introduced to solve a slightly different issue. The > thing is that supplying a fixed voltage SDHCI controller from a variable > regulator is still a valid configuration. Which means that testing the > capabilities of the regulator doesn't actually describe the SDHCI > controller itself. The regulator constraints should reflect this. The constraints aren't the capabilities of the regulator, but the limits on what it is supplying. > > In practice this property is used to communicate whether pad > reconfiguration and voltage switching needs to be performed or not. This > cannot be determined from the absence or presence of the pinctrl > properties either because they naturally won't be there on older dtbs. > > The logic behind this goes like this: if this property is present, > there's no need to perform pad or regulator reconfiguration and UHS > modes can be enabled. If this property is missing then valid pinctrl and > regulator properties are required to enable UHS signaling. This is > implemented in tegra_sdhci_is_uhs_valid() in "[PATCH v2 03/10] mmc: > tegra: Reconfigure pad voltages during voltage switching" > > -Aapo -- 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
