Re: [PATCH v7 14/16] power: sequencing: pcie-m2: Split Bluetooth unit based on interface

On Fri, Jul 24, 2026 at 04:43:23PM +0800, Chen-Yu Tsai wrote:
> Some UART / serdev based Bluetooth drivers need to be able to reset the
> hardware during initialization or recovery. This is not possible with
> the current power sequencing API if a unit is shared between USB and
> UART interfaces.
> 
> For now, split the Bluetooth unit into two, one for each interface.
> This allows either interface to independently toggle the power, with
> the last action prevailing, thereby unbreaking the Qualcomm Bluetooth
> serdev driver. This is also needed for the Realtek Bluetooth serdev
> driver (hci_h5).
> 
> Having independent control from either interface unfortunately means
> that userspace is able to shut down the controller from sysfs using
> the USB port's "disable" setting without the serdev driver knowing
> about it. On the USB side, independent control is also desired, as it
> allows the USB core to power cycle the port/device during faults, and
> for userspace to initiate reset and recovery using the aforementioned
> "disable" setting. However when USB is used, a serdev device is not
> created, and there is no conflicting usage, which allows the power
> sequencing to work even without the split unit.
> 
> Suggested-by: Wei Deng <[email protected]>
> Signed-off-by: Chen-Yu Tsai <[email protected]>
> ---
> Changes since v4:
> - New patch
> 
> This patch is _not_ squashed into the previous to provide clear context
> on the change, and the less than perfect nature of it.
> 
> I think what we need in this case is some sort of lockout. The serdev
> consumer would want "exclusive" access, locking out the USB consumer,
> which can tolerate "shared" access.
> 
> Something similar would be needed for the WiFi if we ever add support
> for SDIO for toggling the state of W_DISABLE#1. At least the SDIO and
> PCIe reset signals are separate.

I don't think PCIe/SDIO suffers from the same issue as USB/BT. But anyhow, I
think it is OK to have this patch as an interim solution, but we should try to
model the BT control in a proper manner. I'd fancy adding TODO instead of XXX in
the comments. But nevertheless,

Reviewed-by: Manivannan Sadhasivam <[email protected]>

- Mani

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