Re: [PATCH] bus: mhi: host: pci_generic: Switch to async power up to avoid boot delays

[Manivannan Sadhasivam]

On Thu, Jan 22, 2026 at 12:53:48AM -0800, Qiang Yu wrote:
> Some modem devices can take significant time (up to 20 secs for sdx75) to
> enter mission mode during initialization. Currently, mhi_sync_power_up()
> waits for this entire process to complete, blocking other driver probes
> and delaying system boot.
> 
> Switch to mhi_async_power_up() so probe can return immediately while MHI
> initialization continues in the background. This eliminates lengthy boot
> delays and allows other drivers to probe in parallel, improving overall
> system boot performance.
> 

This part is fine.

> Add pm_runtime_forbid() in remove path to prevent device suspend during
> driver reinstallation. This issue is specific to async power up: with
> sync power up, pm_runtime_put_noidle() is called after mission mode is
> reached because mhi_sync_power_up() waits for mission mode event. With
> async power up, pm_runtime_put_noidle() is called immediately while power
> up process continues in background, which can cause the device to
> suspend and mhi init fail if pm_runtime_allow() from a previous probe
> is still active.
> 

pm_runtime_forbid() should be called at the start of the remove() callback to
prevent the device from auto suspending during cleanup and to fix the issue you
described above.

So do in a separate patch and add a Fixes tag pointing to the commit that added
the Runtime PM support.

- Mani

> Fixes: 5571519009d0 ("bus: mhi: host: pci_generic: Add SDX75 based modem support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Qiang Yu <qiang.yu@xxxxxxxxxxxxxxxx>
> ---
>  drivers/bus/mhi/host/pci_generic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
> index 0884a384b77fc3f56fa62a12351933132ffc9293..fc0952e46ae5e4854c7165ed60b850729843d458 100644
> --- a/drivers/bus/mhi/host/pci_generic.c
> +++ b/drivers/bus/mhi/host/pci_generic.c
> @@ -1393,7 +1393,7 @@ static int mhi_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  		goto err_unregister;
>  	}
>  
> -	err = mhi_sync_power_up(mhi_cntrl);
> +	err = mhi_async_power_up(mhi_cntrl);
>  	if (err) {
>  		dev_err(&pdev->dev, "failed to power up MHI controller\n");
>  		goto err_unprepare;
> @@ -1447,6 +1447,7 @@ static void mhi_pci_remove(struct pci_dev *pdev)
>  		mhi_soc_reset(mhi_cntrl);
>  
>  	mhi_unregister_controller(mhi_cntrl);
> +	pm_runtime_forbid(&pdev->dev);
>  }
>  
>  static void mhi_pci_shutdown(struct pci_dev *pdev)
> 
> ---
> base-commit: 91a0b0dce350766675961892ba4431363c4e29f7
> change-id: 20260113-mhi_async_probe-a7b0867b6e2e
> 
> Best regards,
> -- 
> Qiang Yu <qiang.yu@xxxxxxxxxxxxxxxx>
> 

-- 
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