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    SubjectRE: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux mappings
    Date
    ...
    > > * The enumerations above should be purely at the level the HW exposes,
    > > i.e. if a UART uses 4 signals (RX, TX, CTS, RTS), and the SoC
    > > configures muxing at a per-pin level, and 6 pins exist which can have
    > > various UART signals mux'd on to them, there should be a "muxable
    > > entity" enumeration for each of the 6 pins, not an enumeration for
    > > each possible combination of assignments of signals to pins, since in
    > > general that number could be extremely large as Richard Zao points out
    > > in his email that was sent right after yours.
    > >
    > Speaking of the model, yes, it's true. But coming to the practical
    > implementation, we may need compromise on whether we need to do a full
    > enumeration.
    >
    > > * pinmux properties in device drivers should list the muxable entities
    > > that they use, and the mux function for each of them.
    > >
    > Following on the example above, we will need something below in SD node to
    > specify each pin and corresponding function selection.
    >
    > usdhc@02194000 { /* uSDHC2 */
    > #pinmux-cells = <2>;
    > // The second cell specify the index of the desired function of
    > given pin
    > pinmux = < &sd2_dat1 0
    > &sd2_dat2 0
    > ... >;
    > status = "okay";
    > };
    >
    > IMO, it's not nice for pinctrl client devices. Though it's true that the
    > muxable entity is pin, what the client device really cares is its pingroup. We
    > should define the pingroup rather than pin for client device to refer to with a
    > phandle. This is just like that pinctrl subsystem api pinmux_get/enable operate
    > on a pingroup as an interface to client device driver, no matter the muxable
    > entity at HW level is a pin or a group.
    >
    +1
    It's just like what the current pinctrl subsystem does:
    the device says "I'm using this function and this pin group, please enable!"
    But no pins are specified.

    Regards
    Dong Aisheng



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