Messages in this thread Patch in this message | | | Subject | Re: [PATCH] dt-bindings: i2c: add bindings for nxp,pca9541 | From | Peter Rosin <> | Date | Mon, 27 Jun 2016 18:27:21 +0200 |
| |
On 2016-06-27 15:17, Guenter Roeck wrote: > On 06/27/2016 03:11 AM, Peter Rosin wrote: >> Fill the gap for this pre-existing driver. >> >> Signed-off-by: Peter Rosin <peda@axentia.se> >> --- >> .../devicetree/bindings/i2c/i2c-arb-pca9541.txt | 33 ++++++++++++++++++++++ >> MAINTAINERS | 1 + >> 2 files changed, 34 insertions(+) >> create mode 100644 Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt >> >> Hi! >> >> I'm wondering about this driver. It is not a trivial device, and yet it >> has historically relied on the i2c core matching the chip w/o vendor >> prefix. This is not ideal. But what to do about the driver implementing >> this in terms of an i2c-mux, somthing which the chip is not; It is an >> i2c arbitrator. It just happens to rely on the i2c mux core also handling >> i2c gates and i2c arbitrators. But that seems like a Linux detail. So I >> don't know what to do here? >> > > The concept of arbitrators didn't exist when I wrote the driver. I would not > have a problem with renaming the file if that is what you are asking for.
No, that was not my issue, I just wanted to document bindings for pca9541, and I didn't like how it turned out.
I don't really care if the bindings doc is named i2c-mux-pca9541.txt (that would match the name of the driver, but it still wouldn't make the chip a mux).
>> That is, the patch - as is - describes something that would be trivial to >> support today, but at the same time it seems to be too tied to Linux. >> >> The problem is that the i2c@0 intermediate node is not really needed, but >> at the same time removing it would cause a disruption for the driver since >> it can't really use the i2c mux core if that node isn't there. I don't >> see a simple way to fix that in the i2c mux core either (but admittedly >> haven't given it too much thought). >> > > The gpio arbitrator uses the same principle as well. Why not just leave it > alone ? Besides, I think it is a good idea to have it, since it groups > the i2c devices behind the chip together. I would not consider that to be > a Linuxism, but a design choice.
The grouping argument would make sense if there was anything outside the group. Also, the required reg property and the extra #address-cells and #size-cells doesn't add anything and just gets in the way, and is indeed the result of Linuxisms leaking back into device trees.
If there were no muxes and this was a new driver, the example bindings would almost certainly have been something like:
i2c-arbitrator@74 { compatible = "nxp,pca9541"; reg = <0x74>;
#address-cells = <1>; #size-cells = <0>;
eeprom@54 { compatible = "at,24c08"; reg = <0x54>; }; };
which I find much nicer.
But, I can't find a way to implement that and keep backwards compatibility with old existing device trees.
Which is why I submitted the patch I did. It documents the pca9541 bindings, something which is lacking, in terms of i2c-mux as the driver is written. At the same time, this feels ugly and exposes linuxism and I wanted to make that clear up front. The above simply looks better than the example in the patch.
I intended to mark the submission [RFC PATCH], but I now realize that that went missing along the way, sorry.
Cheers, Peter
> Guenter > >> Any suggestions? >> >> Cheers, >> Peter >> >> PS. The driver source is in drivers/i2c/muxes/i2c-mux-pca9541.c >> >> diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt >> new file mode 100644 >> index 000000000000..edbe84935906 >> --- /dev/null >> +++ b/Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt >> @@ -0,0 +1,33 @@ >> +* NXP PCA9541 I2C bus master selector >> + >> +Required Properties: >> + >> + - compatible: Must be "nxp,pca9541" >> + >> + - reg: The I2C address of the device. >> + >> + The following required properties are defined externally: >> + >> + - Standard I2C mux properties. See i2c-mux.txt in this directory. >> + - I2C child bus nodes. See i2c-mux.txt in this directory. >> + >> + >> +Example: >> + >> + i2c-arbitrator@74 { >> + compatible = "nxp,pca9541"; >> + #address-cells = <1>; >> + #size-cells = <0>; >> + reg = <0x74>; >> + >> + i2c@0 { >> + #address-cells = <1>; >> + #size-cells = <0>; >> + reg = <0>; >> + >> + eeprom@54 { >> + compatible = "at,24c08"; >> + reg = <0x54>; >> + }; >> + }; >> + }; >> diff --git a/MAINTAINERS b/MAINTAINERS >> index e1b090f86e0d..3dd44d0d166c 100644 >> --- a/MAINTAINERS >> +++ b/MAINTAINERS >> @@ -5521,6 +5521,7 @@ S: Maintained >> F: Documentation/i2c/i2c-topology >> F: Documentation/i2c/muxes/ >> F: Documentation/devicetree/bindings/i2c/i2c-mux* >> +F: Documentation/devicetree/bindings/i2c/i2c-arb* >> F: drivers/i2c/i2c-mux.c >> F: drivers/i2c/muxes/ >> F: include/linux/i2c-mux.h >> >
| |