Re: [PATCH] arm64: dts: qcom: sdm845-oneplus: fix fuel gauge compatible

[Rinat Muhamedgaliev]

On 29/08/2026, Konrad Dybcio wrote:
> If I'm reading that thread right, this IC is on the battery itself (?)
> and it seems to differ across different units / suppliers, would that
> be a good interpretation?

That matches what I found while looking into this. Both the bq27411-G1
and bq27541-G1 datasheets describe them as pack-side fuel gauges meant
for integration into the battery pack itself, alongside the protection
IC, rather than being placed on the phone's mainboard. So it's
plausible that different battery packs (different suppliers or
production batches) could carry a different chip variant, and DT
can't detect that at boot time - the bq27xxx driver picks its register
map purely from the compatible string, with no runtime DeviceType
probing.

I want to be upfront: I only tested this on my own OnePlus 6T
(fajita), by reading DeviceType directly over I2C on that one unit. I
haven't verified whether other fajita/enchilada units report the same
value, so I can't rule out that some devices out there actually do
have a bq27411 and would regress with this patch.

I'm not sure what the right way to handle this is and would appreciate
guidance. A few options I can think of, roughly in order of effort:

- Ask other sdm845-mainline users to report their DeviceType (a quick
  i2cget on 0x55) to get a sense of how common each variant is.
- Leave the fix as-is for now, since it's still strictly correct for
  the tested unit and the previous binding was wrong for it, but note
  the pack-side/per-battery caveat explicitly in the commit message.
- Longer term, add DeviceType autodetection to bq27xxx_battery.c
  itself so the driver picks the right register map at probe time
  instead of relying on a static DT compatible - though that's a
  separate, larger change to the driver, not this DT patch.

Happy to go whichever direction you and the other reviewers think is
right; just didn't want to claim more certainty than I actually have.

Rinat


пт, 28 авг. 2026 г. в 13:05, Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>:
>
> On 8/27/26 1:38 AM, Rinat Muhamedgaliev wrote:
> > The fuel gauge at I2C address 0x55 on OnePlus 6T (fajita) reports
> > DeviceType 0x0541, identifying it as a TI bq27541 rather than bq27411.
> >
> > Binding it as bq27411 selects the wrong register map and produces
> > invalid voltage, state-of-charge, and temperature readings. Use the
> > bq27541 compatible and rename the shared label along with its fajita
> > and enchilada consumers.
> >
> > Tested on OnePlus 6T (fajita): queried DeviceType directly over I2C,
> > built the DTB, booted it once with fastboot boot, then installed a
> > locally built postmarketOS kernel package. Before the change, readings
> > included about 65 V, over 10000% SOC, and -273.1 C. Afterward, the
> > bq27xxx driver bound as ti,bq27541 and reported 3.835 V, 42% SOC, and
> > 33.3 C.
> >
> > Fixes: 12dfb002ca01 ("arm64: dts: qcom: sdm845-oneplus-*: add fuel gauge")
> > Closes: https://gitlab.com/sdm845-mainline/linux/-/issues/36
> > Link: https://gitlab.com/sdm845-mainline/linux/-/merge_requests/148
>
> If I'm reading that thread right, this IC is on the battery itself (?)
> and it seems to differ across different units / suppliers, would that
> be a good interpretation?
>
> Konrad