Re: [PATCH] bus: mhi: host: pci_generic: Fix runtime PM imbalance for no_m3 devices

[Jeff Hugo]

On 8/7/2026 8:33 AM, Alexandra Lu wrote:
> mhi_pci_probe() drops the runtime PM reference taken by local_pci_probe()
> only when the device supports both PME from D3hot and M3, but
> mhi_pci_remove() re-takes it based on PME capability alone, without
> checking no_m3.
>
> For a device that is PME capable and has no_m3 set, probe therefore never
> drops the reference while remove takes an extra one, leaving the runtime
> PM usage count one higher after every bind/unbind cycle.  That is benign
> for the device being removed, since the PCI core resumes it to D0 on
> unbind regardless, but the struct device outlives the binding, so the
> count accumulates across repeated cycles and can end up preventing
> runtime suspend altogether.
>
> Cache no_m3 in the driver's private data, as is already done for
> reset_on_remove, and gate the removal side on it as well.  Unlike
> reset_on_remove it is cached for virtual functions too, because the probe
> side gate tests info->no_m3 for physical and virtual functions alike.
>
> QDU100 is currently the only device that sets no_m3.
>
> Fixes: 0494cf9793b7 ("bus: mhi: host: pci_generic: Disable runtime PM for QDU100")
> Assisted-by: Cursor:claude-opus-5
> Signed-off-by: Alexandra Lu <alexandra.lu@xxxxxxxxx>

Seems sane to me.

Reviewed-by: Jeff Hugo <jeff.hugo@xxxxxxxxxxxxxxxx>