On 09/09/2022 05:03, Chunfeng Yun wrote: > On Wed, 2022-08-31 at 09:03 +0300, Krzysztof Kozlowski wrote: >> On 31/08/2022 06:00, Chunfeng Yun wrote: >>> On Tue, 2022-08-30 at 13:08 +0300, Krzysztof Kozlowski wrote: >>>> On 29/08/2022 05:37, Chunfeng Yun wrote: >>>>> On Fri, 2022-08-26 at 09:36 +0300, Krzysztof Kozlowski wrote: >>>>>> On 26/08/2022 08:36, Chunfeng Yun wrote: >>>>>>> On Tue, 2022-08-23 at 13:24 +0300, Krzysztof Kozlowski >>>>>>> wrote: >>>>>>>> On 22/08/2022 10:07, Chunfeng Yun wrote: >>>>>>>>> On Fri, 2022-08-19 at 15:15 +0300, Krzysztof Kozlowski >>>>>>>>> wrote: >>>>>>>>>> On 19/08/2022 12:13, Chunfeng Yun wrote: >>>>>>>>>>> Add a property to set usb2 phy's pre-emphasis. >>>>>>>>>>> >>>>>>>>>>> Signed-off-by: Chunfeng Yun < >>>>>>>>>>> chunfeng.yun@xxxxxxxxxxxx> >>>>>>>>>>> --- >>>>>>>>>>> Documentation/devicetree/bindings/phy/mediatek,tph >>>>>>>>>>> y.ya >>>>>>>>>>> ml | >>>>>>>>>>> 7 >>>>>>>>>>> +++++++ >>>>>>>>>>> 1 file changed, 7 insertions(+) >>>>>>>>>>> >>>>>>>>>>> diff --git >>>>>>>>>>> a/Documentation/devicetree/bindings/phy/mediatek,tp >>>>>>>>>>> hy.y >>>>>>>>>>> aml >>>>>>>>>>> b/Documentation/devicetree/bindings/phy/mediatek,tp >>>>>>>>>>> hy.y >>>>>>>>>>> aml >>>>>>>>>>> index 848edfb1f677..aee2f3027371 100644 >>>>>>>>>>> --- >>>>>>>>>>> a/Documentation/devicetree/bindings/phy/mediatek,tp >>>>>>>>>>> hy.y >>>>>>>>>>> aml >>>>>>>>>>> +++ >>>>>>>>>>> b/Documentation/devicetree/bindings/phy/mediatek,tp >>>>>>>>>>> hy.y >>>>>>>>>>> aml >>>>>>>>>>> @@ -219,6 +219,13 @@ patternProperties: >>>>>>>>>>> minimum: 1 >>>>>>>>>>> maximum: 15 >>>>>>>>>>> >>>>>>>>>>> + mediatek,pre-emphasis: >>>>>>>>>>> + description: >>>>>>>>>>> + The selection of pre-emphasis (U2 phy) >>>>>>>>>>> + $ref: >>>>>>>>>>> /schemas/types.yaml#/definitions/uint32 >>>>>>>>>>> + minimum: 1 >>>>>>>>>>> + maximum: 3 >>>>>>>>>> >>>>>>>>>> Instead of hard-coding register values in bindings, >>>>>>>>>> you >>>>>>>>>> should >>>>>>>>>> rather >>>>>>>>>> describe here feature/effect. If it is in units, use >>>>>>>>>> unit >>>>>>>>>> suffixes. >>>>>>>>>> If >>>>>>>>>> it is some choice, usually string enum is >>>>>>>>>> appropriate. >>>>>>>>> >>>>>>>>> How about changing description as bellow: >>>>>>>>> >>>>>>>>> "The level of pre-emphasis, increases one level, boosts >>>>>>>>> the >>>>>>>>> relative >>>>>>>>> amplitudes of signal's higher frequencies components >>>>>>>>> about >>>>>>>>> 4.16% >>>>>>>>> (U2 >>>>>>>>> phy)" >>>>>>>>> >>>>>>>> >>>>>>>> Still the question is what is the unit. 4.16%? >>>>>>> >>>>>>> No unit, it's a level value, like an index of array. >>>>>>> >>>>>> >>>>>> So a value from register/device programming? >>>>> >>>>> Yes >>>>>> Rather a regular units >>>>>> should be used if that's possible. If not, this should be >>>>>> clearly >>>>>> described here, not some magical number which you encode into >>>>>> DTS... >>>>> >>>>> Ok, I'll add more descriptions. >>>> >>>> Better use logical value, e.g. >>>> >>> >>> > https://urldefense.com/v3/__https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml*L38__;Iw!!CTRNKA9wMg0ARbw!1e-h0R_uwcaHKfKC9qYfaRWYeuWRq1sLCGy3yupNmkFyuW5s1nmRotL7Y0vFG9ETLLTA$ >>>> >>> >>> Optional unit may be -percent or -bp, but the value 4.16% * X >>> (X=1,2,3...)is not an exact value, they are variable in a range and >>> dependent more factors. >>> So I think use level value is simple enough. >> >> Then again explain exactly what are the levels. How you wrote it last >> time, -bp would do the trick. > > There are many different methods of measuring pre-emphasis. > The way used in MediaTek USB2 PHY as below: > > pre-emphasis level equation = Vpp/Vs -1; > Vpp: peak-peak voltage of differential signal; > Vs : static voltage of differential signal, normal voltage, e.g. 400mV > for u2 phy; > > The pre-emphasis circuitry within t-phy can be dynamically programmed > to three different levels of pre-emphasis. The exact value of > pre-emphasis cannot be predetermined, because each device requires > a percentage of pre-emphasis that is dependent on the output signal > strength and transmission path characteristics. > > Below shows three programmable pre-emphasis levels for a differential > drive signal of 400 mV. The amount of pre-emphasis changes according > to the transmission path parameters. > > programmable level typical pre-emphasis level > 1 4.16% > 2 8.30% > 3 12.40% > > The reasons that why prefer to use programmable level in dt-binding as > following: > 1. as you said, -bp may do the trick, but the main problem is that > pre-emphasis level is variable on different SoC, and is also > variable even on different pcb for the same SoC. e.g. for the > programmable level 1, pre-emphasis level may be 6% on a platform, > but for the programmable level 2, pre-emphasis level may be also > 6% on another platform; > I think use pre-emphasis level in property, e.g. 4.16%, the > deviation may be bigger than 40%, may cause confusion for users, > due to we can't promise that the actual measurement is about 4.16%, > it may be 2%, or 5% when measured; > 2. the programmable / logical level is flexible when we support more > and pre-emphasis level, ans it is easy for us to tune the level > due to it's continuous value. > 3. all other vendor properties that can't provide exact measurable > value in this dt-binding make use of logic level, I want to > keep them align; Hm, that's clarifies a lot. Thanks for explanation. It's ok for me. Best regards, Krzysztof
