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[199.106.103.254]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b70d7f729bsm1680791eec.16.2026.01.20.14.16.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Jan 2026 14:16:18 -0800 (PST) Message-ID: <5cec9127-bdc5-49d7-80e1-2ae26f81163c@oss.qualcomm.com> Date: Tue, 20 Jan 2026 14:16:17 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/9] dt-bindings: soc: qcom: eud: Restructure to model multi-path hardware To: Krzysztof Kozlowski , Bjorn Andersson Cc: Greg Kroah-Hartman , Konrad Dybcio , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Souradeep Chowdhury , linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260116232106.2234978-1-elson.serrao@oss.qualcomm.com> <20260116232106.2234978-2-elson.serrao@oss.qualcomm.com> <20260117-courageous-chamois-of-focus-20d5d5@quoll> <4d6ffe96-2113-42fd-97e5-42247f073aef@kernel.org> Content-Language: en-US From: Elson Serrao In-Reply-To: <4d6ffe96-2113-42fd-97e5-42247f073aef@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTIwMDE4NSBTYWx0ZWRfX6WjfEBcaxoR+ ESfEzC5RtmtSpJGZdWqpbSG5jdpDKBxo8dSudicjMNJjr2j7YfmTQirKdpEGnHz2K3oTHZUx3kh RF2fPFsJ69dnHBRWu1q6mF2XX2aovXEFclJSnSGM/lRRaxyGQ8hYGL2HNZB6nnOibueVSBN4wOG QJRydpoRuoGn2mJAKc9tMEPneFDMewV2XRYAyydBY3zTT6iw6wI4n26gmd4ZXYriNwkM4DxRyVk 325avGodkZDRIa1YBaFkSaSfX9xCBTzjDodoit7ysQUDwUYioHDFgCKtGyzTVAlAryNsyfCsweG ahAqXJV2gpG16iyIoSTfp6fKtin0HqfHKDMQRiWksSgGemi3fjLNPlAXiOBwWtZuG6V+p+IiX0A v81dMHTdaCjbj+khIHatQ12nIKAckadw8XPK1R3b2snFU7/sW36UpVds0YrzkY7twuvMkhCRRP7 HBwfG0mWkmw59AlO6sQ== X-Authority-Analysis: v=2.4 cv=IYeKmGqa c=1 sm=1 tr=0 ts=696ffeb5 cx=c_pps a=cFYjgdjTJScbgFmBucgdfQ==:117 a=JYp8KDb2vCoCEuGobkYCKw==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=esL1I7lv05GZoeN1qSMA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=scEy_gLbYbu1JhEsrz4S:22 X-Proofpoint-GUID: wS8xuqmb24lw2iY0TUtROomSQ_LJGugq X-Proofpoint-ORIG-GUID: wS8xuqmb24lw2iY0TUtROomSQ_LJGugq X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.20,FMLib:17.12.100.49 definitions=2026-01-20_06,2026-01-20_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 adultscore=0 phishscore=0 spamscore=0 impostorscore=0 clxscore=1015 bulkscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2601200185 On 1/19/2026 11:20 PM, Krzysztof Kozlowski wrote: > On 19/01/2026 20:58, Bjorn Andersson wrote: >> On Sat, Jan 17, 2026 at 12:57:58PM +0100, Krzysztof Kozlowski wrote: >>> On Fri, Jan 16, 2026 at 03:20:58PM -0800, Elson Serrao wrote: >>>> The Qualcomm Embedded USB Debugger (EUD) hardware can intercept up to >>>> two independent High-Speed UTMI data paths, depending on the SoC >>>> configuration. Each path operates independently with: >>>> >>>> - Dedicated PHY interface >>>> - Distinct USB connector and controller associations >>>> - Role dependent routing >>>> >>>> Model these hardware paths as separate eud-path nodes to accurately >>>> represent the physical topology and add below per-path properties: >>>> >>>> phys: EUD exposes a High-Speed debug hub that relies on HS-PHY for its >>>> operation. This property references the HS-PHY associated with the UTMI >>>> path. >>>> >>>> usb-role-switch: Indicates that the USB port on this UTMI path supports >>>> role switching. In device role, debug mode inserts the EUD hub into the >>>> UTMI path. In host role, the EUD hub is bypassed and UTMI traffic flows >>>> directly between the PHY and the USB controller. >>>> >>>> This change breaks backwards compatibility, but the previous binding >>>> omitted critical resources like PHY and did not describe per-path >>>> topology. Without these modifications EUD cannot be guaranteed to >>>> function. >>> >>> It was working for 3 years, so your guarantees are just imprecise. FUD >>> is not an argument. >>> >>> Qualcomm task at 2022 was to post complete bindings. These were posted >>> and accepted. Three years later you say that previous posting was >>> bollocks and this cannot even work? >>> >> >> That is correct. The description of the hardware that was provided when >> this was upstreamed and the binding that was accepted based on this >> description is wrong. >> >> There's absolutely a value in maintainting backwards compatibility in >> general, but is this one of those cases? >> >>> Nah, take responsibility of what you did in the past. >>> >> >> In my view the responsible thing is to accept that we got it wrong and >> make sure EUD is enabled end-to-end so people can actually use it. > > I would expect to see what is not working. This is in mainline for three > years, so the assumption is that it was working for these three years. > If it wasn't, this should be described and "cannot be guaranteed to > function" is just imprecise. > Thanks, Bjorn and Krzysztof, for the feedback. Let me clarify what I meant by “cannot be guaranteed to work”, as I agree the phrasing can be improved to more precisely convey the intent. The concern is not that EUD did not or could not work historically. Rather, the issue is that the hardware description provided by the binding does not explicitly describe ownership and control of hardware resources that EUD depends on. As a result, correctness of EUD operation relies on behavior outside of what is expressed in the description. Concretely, the binding does not reference the HS-PHY. In practice, EUD may function because the USB controller (e.g. DWC3) keeps the PHY powered and configured. However, this relationship is not described as a contract in the binding. The USB controller may legitimately relinquish PHY control as part of its own power-management or low-power transitions. The EUD hardware is capable of operating independently, but doing so requires EUD to have explicit control of the PHY. The hardware specification lists the PHY as a required resource of the EUD debug hub. Not modeling it in the binding therefore leaves the description incomplete, because EUD resource requirements are being met implicitly through another hardware block (USB controller) rather than being described directly. In addition, the hardware can expose multiple UTMI paths (dual-port EUD), which the current binding cannot represent. The intent of this patch is therefore to correct and tighten the binding so that the hardware resources and topology EUD depends on are explicitly modeled, rather than relying on side effects of USB controller. I will update the backwards compatibility justification accordingly. Thanks Elson