On Wed, Sep 26, 2018 at 01:25:20PM -0700, Nicolin Chen wrote: > Hello, > > On Wed, Sep 26, 2018 at 12:58:17PM -0700, Guenter Roeck wrote: > > On Wed, Sep 26, 2018 at 11:02:44AM -0700, Nicolin Chen wrote: > > > On Wed, Sep 26, 2018 at 06:06:32AM -0700, Guenter Roeck wrote: > > > > On 09/25/2018 11:42 PM, Nicolin Chen wrote: > > > > > The inX_enable interface allows user space to enable or disable > > > > > the corresponding channel. Meanwhile, according to hwmon ABI, a > > > > > disabled channel/sensor should return -ENODATA as a read result. > > > > > > > > > > However, there're configurable nodes sharing the same __show() > > > > > functions. So this change also adds to check if the attribute is > > > > > read-only to make sure it's not reading a configuration but the > > > > > sensor data. > > > > > > > One necessary high level change I don't see below: With this change, > > > > we should no longer drop a channel entirely if it is disabled from > > > > devicetree. All channels should be visible but report -ENODATA if > > > > disabled. In other words, it should be possible for the 'enable' flag > > > > to override settings in DT. > > > > > > Hmm...I don't feel so convinced here. The status in DT binding isn't > > > exactly a setting but a physical status: if a hardware design leaves > > > a channel to be disconnected, I don't really see a point in enabling > > > it in the runtime. Or maybe you can shed some light on it? > > > > > > > You are making an assumption from your use case. It might as well be that > > some or all channels are disabled in DT by default to conserve power, > > not because they are disconnected. > > I think I probably should update my DT binding somehow to say it > explicitly that the property should be only used in cases of the > physical disconnections, although I feel the current binding "no > input source" already has the same meaning. > > In my opinion, disabling channels in DT to save power isn't very > plausible, because it sounds more likely a user decision, while, > as we know, DT merely describes the hardware design. > I try to avoid making such assumptions. All I know is that I'll have to deal with the fallout if a single person wants to use the property differently. This is similar to disabling an entire subsystem in DT because it isn't used in a specific system - say, a SPI or I2C bus which has nothing connected on some shipping hardware, even though the board has a connector for it. Your argument is that one shall not use the status property do disable loading the driver, and that one must not remove a set of properties for unused hardware either. That doesn't sound very realistic to me. Point is that I don't _know_ how this is going to be used, so I'd rather keep it flexible. Guenter > Otherwise, if we want something like a setting for this purpose, > we should probably use a different property for DT binding, bool > type "disable-on-boot" for example. > > > > Meanwhile, I believe the enable nodes are necessary in either way as > > > users could decide to disable the connected channels, based on their > > > use cases, to save power. > > > > > Agreed, though I would not say "necessary". "Useful" seems to be more > > appropriate. > > Yea..
