| Message ID | af211ec180d91a13862630e635019ebe03d4be31.1677080089.git.mazziesaccount@gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | Support ROHM BU27034 ALS sensor | expand |
On 22/02/2023 17:14, Matti Vaittinen wrote: > ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes > capable of detecting a very wide range of illuminance. Typical application > is adjusting LCD and backlight power of TVs and mobile phones. > > Add initial dt-bindings. Driver can be "initial", but bindings better to be closer to complete, even if not used by the driver currently. > > Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com> > --- > .../bindings/iio/light/rohm-bu27034.yaml | 46 +++++++++++++++++++ > 1 file changed, 46 insertions(+) > create mode 100644 Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml > > diff --git a/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml b/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml > new file mode 100644 > index 000000000000..a3a642c259e8 > --- /dev/null > +++ b/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml Comma as a separator, so: rohm,bu27034.yaml > @@ -0,0 +1,46 @@ > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/iio/light/rohm-bu27034.yaml# With filename and $id fix: Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Best regards, Krzysztof
Hi dee Ho Krzysztof, Thanks for the review! It's nice you had the time to take a look on RFC :) On 2/22/23 20:57, Krzysztof Kozlowski wrote: > On 22/02/2023 17:14, Matti Vaittinen wrote: >> ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes >> capable of detecting a very wide range of illuminance. Typical application >> is adjusting LCD and backlight power of TVs and mobile phones. >> >> Add initial dt-bindings. > > Driver can be "initial", but bindings better to be closer to complete, > even if not used by the driver currently. Out of the curiosity - why is that? (Please, don't take me wrong, I am not trying to argue against this - just learn the reason behind). I can't immediately see the harm caused by adding new properties later when we learn more of hardware. (and no, I don't expect this simple IC to gain at least many properties). >> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com> >> --- >> .../bindings/iio/light/rohm-bu27034.yaml | 46 +++++++++++++++++++ >> 1 file changed, 46 insertions(+) >> create mode 100644 Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml >> >> diff --git a/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml b/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml >> new file mode 100644 >> index 000000000000..a3a642c259e8 >> --- /dev/null >> +++ b/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml > > > Comma as a separator, so: > rohm,bu27034.yaml Oh, yes. So it seems. Strange, I could have sworn I used hyphen in binding file names previously although the comma has been used in the compatible. I had to go back in time (lore,kernel.org) to check my earlier submissions. Well, my mind seems to be playing tricks on me @_@. I'll fix this before sending out non RFC series :) Good catch (as always)! Thanks! >> @@ -0,0 +1,46 @@ >> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) >> +%YAML 1.2 >> +--- >> +$id: http://devicetree.org/schemas/iio/light/rohm-bu27034.yaml# > > With filename and $id fix: > > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> > > > Best regards, > Krzysztof >
On 23/02/2023 07:20, Vaittinen, Matti wrote: > Hi dee Ho Krzysztof, > > Thanks for the review! It's nice you had the time to take a look on RFC :) > > On 2/22/23 20:57, Krzysztof Kozlowski wrote: >> On 22/02/2023 17:14, Matti Vaittinen wrote: >>> ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes >>> capable of detecting a very wide range of illuminance. Typical application >>> is adjusting LCD and backlight power of TVs and mobile phones. >>> >>> Add initial dt-bindings. >> >> Driver can be "initial", but bindings better to be closer to complete, >> even if not used by the driver currently. > > Out of the curiosity - why is that? (Please, don't take me wrong, I am > not trying to argue against this - just learn the reason behind). I > can't immediately see the harm caused by adding new properties later > when we learn more of hardware. (and no, I don't expect this simple IC > to gain at least many properties). Linux drivers change, but the hardware does not, thus DTS, which describes the hardware, can be complete. It should be written based on the hardware, not based on Linux drivers. If you add incomplete bindings, this suggests you wrote them to match your driver, not to match hardware. This in turn (adjusting bindings to driver) makes them less portable, narrowed to one specific driver implementation and more ABI-break-prone later. Imagine you that clock inputs, which you skipped in the binding, were actually needed but on your board they were enabled by bootloader. The binding is then used on other systems or by out of tree users. On your new system the clocks are not enabled by bootloader anymore, thus you add them to the binding. They are actually required for device to work, so you make them required. But all these other users cannot be fixed... What's more, incomplete binding/DTS is then used together with other pieces - DTS and driver, e.g. via some graphs or other phandles/supplies/pinctrl. So some other DTS or driver code might rely on your particular binding. Imagine you had only vdd-supply regulator, but no reset pins, so the only way to power-cycle device was to turn off/on regulator supply. Then you figure out that you have reset pins and it would be useful to add and use it. But already drivers are written to power cycle via regulator... or even someone wrote new driver regulator-pwrseq to power cycle your device due to missing reset GPIOs... Best regards, Krzysztof
On 2/23/23 11:26, Krzysztof Kozlowski wrote: > On 23/02/2023 07:20, Vaittinen, Matti wrote: >> On 2/22/23 20:57, Krzysztof Kozlowski wrote: >>> On 22/02/2023 17:14, Matti Vaittinen wrote: >>>> ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes >>>> capable of detecting a very wide range of illuminance. Typical application >>>> is adjusting LCD and backlight power of TVs and mobile phones. >>>> >>>> Add initial dt-bindings. >>> >>> Driver can be "initial", but bindings better to be closer to complete, >>> even if not used by the driver currently. >> >> Out of the curiosity - why is that? (Please, don't take me wrong, I am >> not trying to argue against this - just learn the reason behind). I >> can't immediately see the harm caused by adding new properties later >> when we learn more of hardware. (and no, I don't expect this simple IC >> to gain at least many properties). > > Linux drivers change, but the hardware does not, thus DTS, which > describes the hardware, can be complete. It should be written based on > the hardware, not based on Linux drivers. If you add incomplete > bindings, this suggests you wrote them to match your driver, not to > match hardware. This in turn (adjusting bindings to driver) makes them > less portable, narrowed to one specific driver implementation and more > ABI-break-prone later. > > Imagine you that clock inputs, which you skipped in the binding, were > actually needed but on your board they were enabled by bootloader. The > binding is then used on other systems or by out of tree users. On your > new system the clocks are not enabled by bootloader anymore, thus you > add them to the binding. They are actually required for device to work, > so you make them required. But all these other users cannot be fixed... > > What's more, incomplete binding/DTS is then used together with other > pieces - DTS and driver, e.g. via some graphs or other > phandles/supplies/pinctrl. So some other DTS or driver code might rely > on your particular binding. Imagine you had only vdd-supply regulator, > but no reset pins, so the only way to power-cycle device was to turn > off/on regulator supply. Then you figure out that you have reset pins > and it would be useful to add and use it. But already drivers are > written to power cycle via regulator... or even someone wrote new driver > regulator-pwrseq to power cycle your device due to missing reset GPIOs... Thanks for explanation Krzysztof. I think that what you wrote here makes sense. Still, I don't think this "adding features only later can cause problems to others" is in any way fundamentally different for bindings and software. Sure this clock example is a valid thing, adding a clock later could cause kernel to suddenly be aware of it can disable it - but disabling the clock would still require a new piece of clk driver too... I think same problems can happen when lower layer SW does not implement all the features - upper layers may need to implement some odd quircks and workarounds to get things working, and all that can be useless or even incompatible with the new low-level SW which finally adds the missing implementation. I guess the 'fundamental' difference I was looking for is that the hardware itself should not change - so in theory we should know the HW from the day 1. Still, we (I) at times notice we need some information about the hardware only when we are (I am) writing the drivers ;) Unfortunately there are companies where all the information about the hardware is not immediately available ... Out of the curiosity 2 (an no need to respond if you're in hurry) - how should one treat hardware logic which is implemented on FPGA? I have in the past worked for a good while on a project where FPGA blocks were also described in dt - but this _really_ blurs the line between "immutable" hardware and "mutable" software. (And yes, we had a great deal of "fun" with updating the FPGA images, FPGA device-trees, linux images and board device-trees...) Anyways, I agree with you. It would be good to have as complete bindings as possible from the day 1. By the way - planning to attend ELCE next summer? It'd be great to have a lecture part II about writing the bindings ;) Yours, --Matti
On Thu, 23 Feb 2023 10:26:02 +0100 Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> wrote: > On 23/02/2023 07:20, Vaittinen, Matti wrote: > > Hi dee Ho Krzysztof, > > > > Thanks for the review! It's nice you had the time to take a look on RFC :) > > > > On 2/22/23 20:57, Krzysztof Kozlowski wrote: > >> On 22/02/2023 17:14, Matti Vaittinen wrote: > >>> ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes > >>> capable of detecting a very wide range of illuminance. Typical application > >>> is adjusting LCD and backlight power of TVs and mobile phones. > >>> > >>> Add initial dt-bindings. > >> > >> Driver can be "initial", but bindings better to be closer to complete, > >> even if not used by the driver currently. > > > > Out of the curiosity - why is that? (Please, don't take me wrong, I am > > not trying to argue against this - just learn the reason behind). I > > can't immediately see the harm caused by adding new properties later > > when we learn more of hardware. (and no, I don't expect this simple IC > > to gain at least many properties). > > Linux drivers change, but the hardware does not, thus DTS, which > describes the hardware, can be complete. It should be written based on > the hardware, not based on Linux drivers. If you add incomplete > bindings, this suggests you wrote them to match your driver, not to > match hardware. This in turn (adjusting bindings to driver) makes them > less portable, narrowed to one specific driver implementation and more > ABI-break-prone later. > > Imagine you that clock inputs, which you skipped in the binding, were > actually needed but on your board they were enabled by bootloader. The > binding is then used on other systems or by out of tree users. On your > new system the clocks are not enabled by bootloader anymore, thus you > add them to the binding. They are actually required for device to work, > so you make them required. But all these other users cannot be fixed... > > What's more, incomplete binding/DTS is then used together with other > pieces - DTS and driver, e.g. via some graphs or other > phandles/supplies/pinctrl. So some other DTS or driver code might rely > on your particular binding. Imagine you had only vdd-supply regulator, > but no reset pins, so the only way to power-cycle device was to turn > off/on regulator supply. Then you figure out that you have reset pins > and it would be useful to add and use it. But already drivers are > written to power cycle via regulator... or even someone wrote new driver > regulator-pwrseq to power cycle your device due to missing reset GPIOs... To add one wrinkle here, board designers have an annoying habit of not wiring reset pins up so if there is any easy way to support an alternative (often there is a software reset command over a bus) then keep the reset pins as optional and implement that in the driver from day one. Same is true of interrupts, though that can be harder to deal with so the binding may say they are optional but the driver fail to load without them. Nice reply Krzyzstof, I'll try and remember to point people at this one as the question comes up pretty often. Thanks, Jonathan > > > Best regards, > Krzysztof >
diff --git a/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml b/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml new file mode 100644 index 000000000000..a3a642c259e8 --- /dev/null +++ b/Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml @@ -0,0 +1,46 @@ +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/iio/light/rohm-bu27034.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: ROHM BU27034 ambient light sensor + +maintainers: + - Matti Vaittinen <mazziesaccount@gmail.com> + +description: | + ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes + capable of detecting a very wide range of illuminance. Typical application + is adjusting LCD and backlight power of TVs and mobile phones. + https://fscdn.rohm.com/en/products/databook/datasheet/ic/sensor/light/bu27034nuc-e.pdf + +properties: + compatible: + const: rohm,bu27034 + + reg: + maxItems: 1 + + vdd-supply: true + +required: + - compatible + - reg + +additionalProperties: false + +examples: + - | + i2c { + #address-cells = <1>; + #size-cells = <0>; + + light-sensor@38 { + compatible = "rohm,bu27034"; + reg = <0x38>; + vdd-supply = <&vdd>; + }; + }; + +...
ROHM BU27034 is an ambient light sesnor with 3 channels and 3 photo diodes capable of detecting a very wide range of illuminance. Typical application is adjusting LCD and backlight power of TVs and mobile phones. Add initial dt-bindings. Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com> --- .../bindings/iio/light/rohm-bu27034.yaml | 46 +++++++++++++++++++ 1 file changed, 46 insertions(+) create mode 100644 Documentation/devicetree/bindings/iio/light/rohm-bu27034.yaml