Hi, On Tue, Apr 10, 2018 at 12:16 AM, Manu Gautam <mgautam@xxxxxxxxxxxxxx> wrote: > > > On 4/10/2018 1:48 AM, Rob Herring wrote: >> On Thu, Mar 29, 2018 at 01:38:23PM -0700, Doug Anderson wrote: >>> Hi, >>> >>> On Thu, Mar 29, 2018 at 4:04 AM, Manu Gautam <mgautam@xxxxxxxxxxxxxx> wrote: >>>> To improve eye diagram for PHYs on different boards of same SOC, >>>> some parameters may need to be changed. Provide device tree >>>> properties to override these from board specific device tree >>>> files. While at it, replace "qcom,qusb2-v2-phy" with compatible >>>> string for USB2 PHY on sdm845 which was earlier added for >>>> sdm845 only. >>>> >>>> Signed-off-by: Manu Gautam <mgautam@xxxxxxxxxxxxxx> >>>> --- >>>> .../devicetree/bindings/phy/qcom-qusb2-phy.txt | 19 ++++++++++++++++++- >>>> 1 file changed, 18 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/Documentation/devicetree/bindings/phy/qcom-qusb2-phy.txt b/Documentation/devicetree/bindings/phy/qcom-qusb2-phy.txt >>>> index 42c9742..0ed140a 100644 >>>> --- a/Documentation/devicetree/bindings/phy/qcom-qusb2-phy.txt >>>> +++ b/Documentation/devicetree/bindings/phy/qcom-qusb2-phy.txt >>>> @@ -6,7 +6,7 @@ QUSB2 controller supports LS/FS/HS usb connectivity on Qualcomm chipsets. >>>> Required properties: >>>> - compatible: compatible list, contains >>>> "qcom,msm8996-qusb2-phy" for 14nm PHY on msm8996, >>>> - "qcom,qusb2-v2-phy" for QUSB2 V2 PHY. >>>> + "qcom,sdm845-qusb2-phy" for 10nm PHY on sdm845. >>>> >>>> - reg: offset and length of the PHY register set. >>>> - #phy-cells: must be 0. >>>> @@ -27,6 +27,23 @@ Optional properties: >>>> tuning parameter value for qusb2 phy. >>>> >>>> - qcom,tcsr-syscon: Phandle to TCSR syscon register region. >>> Just to confirm: the new properties below work just fine on the old >>> msm8996 PHY too, right? > No it won't as register layouts and bit fields are different. Also IMP_CTRL > register doesnt exist for msm8996. I will mention that explicitly here. Thanks! Yeah, definitely document which properties only work on sdm845 and which ones work everywhere. >>>> + - qcom,imp-res-offset-value: It is a 6 bit value that specifies offset to be >>>> + added to PHY refgen RESCODE via IMP_CTRL1 register. It is a PHY >>>> + tuning paramter that may vary for different boards of same SOC. >>>> + - qcom,hstx-trim-value: It is a 4 bit value that specifies tuning for HSTX >>>> + output current. 0x0 value corresponding to 24mA which is maximum >>>> + current and 0xf corresponds to lowest current which is 15mA. >>>> + - qcom,preemphasis-level: It is a 2 bit value that specifies pre-emphasis level. >>>> + Possible values are: >>>> + 00: NONE >>>> + 01: +5% >>>> + 10: +10% >>>> + 11: +15% >>> The user of the device tree will expect to specify this in decimal, >>> right? So list the above as 0, 1, 2, 3. ...not 00, 01, 10, 11. > Fine. >>> (though below I suggest that specifying 0, 1, 2, 3 is probably not >>> quite the right way to describe this property). >>> >>> >>>> +- qcom,preemphasis-width: It is a 1 bit value that specifies how long the HSTX >>>> + pre-emphasis (specified using qcom,preemphasis-level) must be in >>>> + effect. Possible values are: >>>> + 0: Full-bit width >>>> + 1: Half-bit width >>> Perhaps just make this a boolean property. If it exists then you get >>> the non-default case. AKA: if the default is full bit width, then >>> you'd allow a boolean property "qcom,preemphasis-half-width" to >>> override. If the default is half bit width then you'd allow >>> "qcom,preemphasis-full-width" to override. > > Default property value for an SOC is specified in driver and could vary from > soc to soc. Hence, from board devicetree for different SOCs we might need > to select separate widths overriding default driver values. > Alternative is to have two bool properties each for half and full-width. Did > you actually mean that? It's OK to keep it as-is then. ...but please document what the default is for every SoC/port combination that supports this property. >>> For all the above optional bits, please indicate what the default is >>> if they aren't specified. If you have to specify a different default >>> for sdm845 vs. msm8996 then so be it (though it would be nice to avoid >>> it by changing the default for sdm845 unless that's totally crazy). > Sure. >>> >>> >>> Overall this looks pretty good to me. Certainly the descriptions are >>> very understandable and this will make tuning on a per-board / >>> per-port basis much easier! Thanks! >>> >>> >>> One last overall comment is that ideally we could make the device tree >>> a little bit more human readable. Right now we'll have a set of >>> properties that looks like this (numbers made up): >>> >>> qcom,imp-res-offset-value = <0x13>; >>> qcom,hstx-trim-value = <0x7>; >>> qcom,preemphasis-level = <1>; >>> qcom,preemphasis-width = <0>; >>> >>> >>> One option to make that more readable would be to change the units, AKA: >>> >>> qcom,hstx-trim-ma = <18>; >>> qcom,preemphasis-percent = <5>; >>> >>> ...then the code would translate from these human-readable values to >>> the real numbers. >> Yes, we often do that. However, there properties are very specific to >> this device and making the driver translate back to h/w values doesn't >> add much. > > Thanks for review Rob. I too agree with both the viewpoints. > Doug, if it is not of much concern then can I stick with current approach? I certainly would appreciate the #defines and believe they add to the readability, but if you're dead set against it and Rob says it's OK, I won't yell too loudly. >>> Another option would be to add a #include to the bindings. I'd defer >>> to the wisdom of the bindings guys about if this is better or worse >>> than adding the units, but personally I like it better because: >>> * You get a compile-time error if you use an unsupported value. >>> * You don't need to add the code to translate. >> This is fine for me. Really, I'm fine with it as-is, but #defines make >> some people happy. >> >> Rob -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
