linux-kernel - Re: [PATCH] usb: host: xhci-mtk: avoid runtime suspend when removing hcd

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Date:   Wed, 3 Jun 2020 14:47:01 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Macpaul Lin <macpaul.lin@...iatek.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     Mediatek WSD Upstream <wsd_upstream@...iatek.com>,
        Macpaul Lin <macpaul.lin@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-usb@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] usb: host: xhci-mtk: avoid runtime suspend when removing
 hcd

On 29.5.2020 7.29, Macpaul Lin wrote:
> When runtime suspend was enabled, runtime suspend might happened
> when xhci is removing hcd. This might cause kernel panic when hcd
> has been freed but runtime pm suspend related handle need to
> reference it.
> 
> Change-Id: I70a5dc8006207caeecbac6955ce8e5345dcc70e6
> Signed-off-by: Macpaul Lin <macpaul.lin@...iatek.com>
> ---
>  drivers/usb/host/xhci-mtk.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-mtk.c b/drivers/usb/host/xhci-mtk.c
> index bfbdb3c..641d24e 100644
> --- a/drivers/usb/host/xhci-mtk.c
> +++ b/drivers/usb/host/xhci-mtk.c
> @@ -587,6 +587,9 @@ static int xhci_mtk_remove(struct platform_device *dev)
>  	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
>  	struct usb_hcd  *shared_hcd = xhci->shared_hcd;
>  
> +	pm_runtime_put_sync(&dev->dev);

Might runtime suspend here.
It's a lot better than before, no panic as hcd isn't released, but a bit unnecessary.

how about this sequence instead:
pm_runtime_disable()
pm_runtime_put_noidle()

> +	pm_runtime_disable(&dev->dev);
> +

-Mathias