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

[Dmitry Baryshkov]

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