Re: [PATCH 3/3] power: sequencing: pcie-m2: Deassert W_DISABLE2# when no UART serdev is created

[Manivannan Sadhasivam]

On Mon, Jul 13, 2026 at 02:46:16PM +0530, Wei Deng wrote:
> On Thu, 9 Jul 2026, Dmitry Baryshkov wrote:
> > On Thu, Jul 09, 2026 at 12:59:42PM +0530, Wei Deng wrote:
> > > The pwrseq_m2_pci_ids[] table lists PCIe BT devices that use UART as the
> > > BT transport and need a UART serdev created by the driver. When a PCIe
> > > device under the M.2 connector does not match any entry in this table,
> > > no UART serdev is created.
> > > 
> > > However, the BT subsystem of such a device may still require W_DISABLE2#
> > > to be deasserted to power up. Rather than adding every possible non-UART
> > > BT device ID to the table, add an else branch that deasserts W_DISABLE2#
> > > whenever a PCIe device is detected under the connector but does not match
> > > a UART BT entry. This allows any BT interface on the card (USB or other)
> > > to enumerate without requiring explicit knowledge of its device ID.
> > > 
> > > The primary use case is USB BT variants of combo chips that share the
> > > same PCIe device ID as their UART counterpart (e.g. WCN7851 NCM865 USB,
> > > sub 0x3378, vs NCM865A UART, sub 0x337c): no UART serdev is needed, but
> > > W_DISABLE2# must be deasserted so the USB BT device can enumerate.
> > 
> > Instead of forcibly toggling it, would it be more sensible to tie pwrseq
> > into the USB too? The onboard-usb-dev implements the same idea (of
> > powering up the USB device), but it predates pwrseq.
> > 
> > > Reassert W_DISABLE2# symmetrically when the PCIe device is removed.
> > > 
> > > Validated on Hamoa EVK (IQ-X7181-EVK) with WCN7851 NCM865 USB card
> > > (sub 0x3378): without this change GPIO116 (W_DISABLE2#) stays low and
> > > no BT interface appears; with this change GPIO116 is driven high and the
> > > USB BT device enumerates and comes up via btusb.
> > > 
> > > Signed-off-by: Wei Deng <wei.deng@xxxxxxxxxxxxxxxx>
> > > ---
> > >  drivers/power/sequencing/pwrseq-pcie-m2.c | 33 +++++++++++++++++++++----------
> > >  1 file changed, 23 insertions(+), 10 deletions(-)
> > > 
> > 
> > -- 
> > With best wishes
> > Dmitry
> > 
> 
> Hi Dmitry,
> 
> There is a patch series from Chen-Yu Tsai that appears to implement what
> you suggested:
> 
>   [PATCH v4 00/14] arm64: mediatek: Add M.2 E-key slot on Chromebooks
>   https://lore.kernel.org/all/20260709095726.704448-1-wenst@xxxxxxxxxxxx/
> 
> We have been testing this on the Qualcomm Hamoa IoT EVK with both UART BT
> and USB BT M.2 cards.  Is this the direction you had in mind?
> 

IMO, we should move towards Chen's series.

- Mani

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