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Tue, 13 Sep 2022 23:33:33 -0700 Received: from mtkcas11.mediatek.inc (172.21.101.40) by mtkmbs10n2.mediatek.inc (172.21.101.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.792.3; Wed, 14 Sep 2022 13:42:58 +0800 Received: from mhfsdcap04 (10.17.3.154) by mtkcas11.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Wed, 14 Sep 2022 13:42:55 +0800 Message-ID: <207b8c4ef0999a7b859c5e2eaf270293d2f18f75.camel@mediatek.com> Subject: Re: [PATCH 2/7] dt-bindings: phy: mediatek,tphy: add property to set pre-emphasis From: Chunfeng Yun To: Krzysztof Kozlowski , Vinod Koul , Rob Herring CC: Kishon Vijay Abraham I , Krzysztof Kozlowski , Matthias Brugger , , , , , , Eddie Hung Date: Wed, 14 Sep 2022 13:42:55 +0800 In-Reply-To: <8090e2e1-afce-9341-2ae7-3f4e094409b6@linaro.org> References: <20220819091344.2274-1-chunfeng.yun@mediatek.com> <20220819091344.2274-2-chunfeng.yun@mediatek.com> <438da392-f419-ad76-7e91-aa4aab36e12c@linaro.org> <816ecf6287533137b750c8bde9de5830e4229c56.camel@mediatek.com> <1a16cce9fe164bafc06ae193310be71c6f645d75.camel@mediatek.com> <000babd8-5980-3d77-f156-324b3442cbe7@linaro.org> <114c357f8d7f049d21ede789a292a8e2d45f4c61.camel@mediatek.com> <0a82842d-283c-e266-84f4-6306f29b61da@linaro.org> <8dcb4de53a52ab44d40f490099b6ed13e5ef7fe0.camel@mediatek.com> <3c180570-ecf9-3db4-c698-39c1b4679c6e@linaro.org> <3b18a9c687af38f7299261c9a589ef3dfc5a1aa7.camel@mediatek.com> <8090e2e1-afce-9341-2ae7-3f4e094409b6@linaro.org> X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220913_233335_748425_FE8A661E X-CRM114-Status: GOOD ( 44.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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@mediatek.com> > > > > > > > > > > > > --- > > > > > > > > > > > > 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel