On Fri, 2022-09-09 at 10:27 +0200, Krzysztof Kozlowski wrote: > 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/mediate > > > > > > > > > > > > k,tp > > > > > > > > > > > > hy.y > > > > > > > > > > > > aml > > > > > > > > > > > > b/Documentation/devicetree/bindings/phy/mediate > > > > > > > > > > > > k,tp > > > > > > > > > > > > hy.y > > > > > > > > > > > > aml > > > > > > > > > > > > index 848edfb1f677..aee2f3027371 100644 > > > > > > > > > > > > --- > > > > > > > > > > > > a/Documentation/devicetree/bindings/phy/mediate > > > > > > > > > > > > k,tp > > > > > > > > > > > > hy.y > > > > > > > > > > > > aml > > > > > > > > > > > > +++ > > > > > > > > > > > > b/Documentation/devicetree/bindings/phy/mediate > > > > > > > > > > > > k,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. I couldn't know more about pre-emphasis without your questions, thank you very much. > It's ok for me. > > > Best regards, > Krzysztof
