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

[Wei Deng]

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?

Thanks,
Wei Deng

-- 
Best Regards,
Wei Deng