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([2a00:79e0:2e7c:8:2e25:e54f:a73c:729d]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3081e48c3dcsm5106983eec.1.2026.06.12.13.50.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Jun 2026 13:50:08 -0700 (PDT) Message-ID: Date: Fri, 12 Jun 2026 13:50:06 -0700 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 0/2] Add support for Battery Status AMS From: Amit Sunil Dhamne To: Sebastian Reichel Cc: Badhri Jagan Sridharan , Heikki Krogerus , Greg Kroah-Hartman , Hans de Goede , Krzysztof Kozlowski , Marek Szyprowski , Sebastian Krzyszkowiak , Purism Kernel Team , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, =?UTF-8?Q?Andr=C3=A9_Draszik?= , Tudor Ambarus , Peter Griffin , RD Babiera , Kyle Tso References: <20260602-batt-status-v3-0-a7c1c271f3b0@google.com> <6ea3d71f-ec81-44b7-a0f7-d10adcb4c834@google.com> Content-Language: en-US In-Reply-To: <6ea3d71f-ec81-44b7-a0f7-d10adcb4c834@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Sebastian, On 6/8/26 12:20 PM, Amit Sunil Dhamne wrote: > Hi Sebastian, > > On 6/4/26 10:36 AM, Sebastian Reichel wrote: >> Hi, >> >> On Tue, Jun 02, 2026 at 10:47:05PM +0000, Amit Sunil Dhamne via B4 Relay wrote: >>> PD 3.1 v1.8 Spec necessitates a response to Get_Battery_Status request >>> from the port partner (see "6.13.2 Applicability of Data Message"). >>> This patchset adds support to get all the battery type power supplies >>> and query them to report the telemetry required to build a Battery >>> Status Message. Right now, this submission assumes all the battery type >>> power supplies that exist in the system are fixed (meaning cannot be hot >>> swapped). >>> >>> Previously, I had sent a patch series [1]. However there were some >>> concerns. Broadly: >>> * No client drivers >>> * Duplicating dt properties >>> To address the above issues, we now have Fuel Gauge and Charger drivers. >>> Also, I have rectified my approach to fetch information about batteries >>> from the power supply core. >>> >>> While, the original patch series [1] added support for Battery Caps as >>> well, this patch series only adds support for Battery Status. Therefore, >>> I am sending it as a new series while incorporating relevant feedback. >>> >>> [1] https://lore.kernel.org/all/20250507-batt_ops-v2-0-8d06130bffe6@google.com/ >>> >>> Patches in series: >>> [A] "power: supply: Add helpers to get and put arrays of power supply handles" >>> [B] "usb: typec: tcpm: Add support for Battery Status response message" >>> >>> Technical dependency of patches: >>> [B] depends on [A] due to usage of `power_supply_get_battery_all` & >>> `power_supply_put_battery_all` APIs. >>> >>> Signed-off-by: Amit Sunil Dhamne >>> --- >> I think you want to filter on batteries that are >> POWER_SUPPLY_SCOPE_SYSTEM? Otherwise this would also give you >> battery devices for something like a cordless mouse. > Thanks for pointing that out. Which one would you prefer?: > > 1. Bake this into the power_supply_get_battery_all() implementation by > either passing the scope as an argument or directly implementing the > filtering on POWER_SUPPLY_SCOPE_SYSTEM without the argument. > > 2. power_supply_get_battery_all() returns all battery type power > supplies but tcpm filters them. Note that tcpm still keeps all > references to all batteries because of the review comments in [2]. > > > [2] > https://lore.kernel.org/all/4e4a63a4-9d07-4b77-a8dc-ba19c9a803f7@kernel.org/ > >> You mention that this is assuming batteries to be always present, >> but handle POWER_SUPPLY_PROP_PRESENT. So basically a battery, which >> has POWER_SUPPLY_PROP_PRESENT=0 would violate the PD spec as Fixed >> Batteries are not supposed to have this unset? > Just to clarify, I meant fixed and not "always present". The spec > defines fixed battery as: > > "A Battery that is not easily removed or replaced by an end user e.g., > requires a special tool to access or is soldered in." > > Theoretically, you could still have a phone with the fixed battery > removed and the system powered by USB. > > So, while this is more relevant to hot-swappable battery case (, which > is defined by the spec as: "A Battery that is easily accessible for a > user to remove or change for another Battery.") it wouldn't be totally > off the mark to add that check here. > > So while I lean on having the check present, I am okay either way. > > >> Not sure if this is fixable, but you implicitly rely on the battery >> driver to be probed before TCPM reaches this. > > Given the power supply architecture, the probe order is deterministic: a > power supplier driver (e.g., the TCPC) must probe before the supplied > devices (charger, fuel-gauge). Because of this, TCPM will naturally be > up and running before the fuel gauge during early boot. > > Holding off TCPM interactions to wait for downstream devices to probe > isn't a viable option. TCPM operates under strict USB-PD timing > constraints. Stalling the state machine to wait for a fuel gauge could > violate these timings and cause the PD contract to fail entirely. > Furthermore, a fuel gauge is not required to establish a valid PD > contract; Battery Status and Battery Cap messages are purely telemetry. > > The current approach handles this cleanly: > (1) If a request comes in during early boot before the battery is > available, we safely send an unsupported message. > (2) The port partner will continue to retry for battery status/caps > irrespective of the reply. > (3) Once the system is fully booted and the fuel gauge has probed, the > telemetry is reported correctly. > > We initially considered a DT-property based approach so TCPM would know > the exact number of batteries (and their reference phandles) at probe > time, but we moved away from that to avoid duplicating DT properties > (based on feedback in [1]). The current implementation safely > prioritizes critical power negotiation over optional telemetry while > still fulfilling the PD requirements in the steady state. > > > Thanks, > > Amit I want to gently follow up on this discussion :) . Looking forward to hearing your feedback on the open threads above. Thanks, Amit > > >> Greetings, >> >> -- Sebastian