On Wed, 24 Oct 2012, Stephen Warren wrote: > Device tree files always need a completely specific value in the > compatible property, even when less-specific/more-generic values are > also present. So for example, the Linux driver might only care about the > following existing: > > compatible = "usb-ehci". > > However, any actual EHCI controller is always some specific model, so > the compatible value must define which specific model it is, e.g.: > > compatible = "nvidia,tegra20-ehci", "usb-ehci". > > Now lets say the Tegra30 EHCI controller is identical to the Tegra20 > controller. That needs to be explicitly represented too: > > compatible = "nvidia,tegra30-ehci", "nvidia,tegra20-ehci", "usb-ehci". > > In that case, the driver might still only declare support for > "nvidia,tegra20-ehci", but "nvidia,tegra30-ehci" is added to be explicit > about the actual HW model. > > This doesn't continue forever though; you typically only list the > specific HW model, the base specific model it's compatible with, and any > generic value needed. So, a hypothetical Tegra40 EHCI controller would be: > > compatible = "nvidia,tegra40-ehci", "nvidia,tegra20-ehci", "usb-ehci". > > Given that, there is always something to key any newly required quirk > off, so even if the need for a quirk is found later, the device tree > already contains the information needed to trigger it. Okay. It appears that quite a few .dts/.dtsi files mention "usb-ehci", for no apparent reason (given that the drivers don't list it): [stern@iolanthe usb-3.6]$ find arch -name '*.dts*' | xargs grep usb-ehci arch/mips/cavium-octeon/octeon_3xxx.dts: compatible = "cavium,octeon-6335-ehci","usb-ehci"; arch/mips/cavium-octeon/octeon_68xx.dts: compatible = "cavium,octeon-6335-ehci","usb-ehci"; arch/arm/boot/dts/tegra20.dtsi: compatible = "nvidia,tegra20-ehci", "usb-ehci"; arch/arm/boot/dts/tegra20.dtsi: compatible = "nvidia,tegra20-ehci", "usb-ehci"; arch/arm/boot/dts/tegra20.dtsi: compatible = "nvidia,tegra20-ehci", "usb-ehci"; arch/arm/boot/dts/at91sam9x5.dtsi: compatible = "atmel,at91sam9g45-ehci", "usb-ehci"; arch/arm/boot/dts/spear13xx.dtsi: compatible = "st,spear600-ehci", "usb-ehci"; arch/arm/boot/dts/spear13xx.dtsi: compatible = "st,spear600-ehci", "usb-ehci"; arch/arm/boot/dts/spear3xx.dtsi: compatible = "st,spear600-ehci", "usb-ehci"; arch/arm/boot/dts/spear600.dtsi: compatible = "st,spear600-ehci", "usb-ehci"; arch/arm/boot/dts/spear600.dtsi: compatible = "st,spear600-ehci", "usb-ehci"; arch/arm/boot/dts/at91sam9g45.dtsi: compatible = "atmel,at91sam9g45-ehci", "usb-ehci"; arch/powerpc/boot/dts/wii.dts: compatible = "nintendo,hollywood-usb-ehci", arch/powerpc/boot/dts/wii.dts: "usb-ehci"; arch/powerpc/boot/dts/sequoia.dts: compatible = "ibm,usb-ehci-440epx", "usb-ehci"; arch/powerpc/boot/dts/canyonlands.dts: compatible = "ibm,usb-ehci-460ex", "usb-ehci"; Is there a real reason that I'm not aware of? Or can all these entries safely be removed? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
