linux-kernel - Re: [RFC PATCH] xhci: do not halt the secondary HCD

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Date:   Mon, 19 Sep 2016 13:22:46 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Joel Stanley <joel@....id.au>, linux-usb@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: [RFC PATCH] xhci: do not halt the secondary HCD

Hello.

On 9/19/2016 9:35 AM, Joel Stanley wrote:

> We can't halt the secondary HCD, because it's also the primary HCD,
> which will cause problems if we have devices attached to the primary
> HCD, like a keyboard.
>
> We've been carrying this in our Linux-as-a-bootloader environment for a little
> while now. The machines all have the same TI TUSB73x0 part, and when we kexec
> the devices don't come back until a system power cycle.
>
> I'd like some advice on an acceptable way to upstream the fix, so that the xhci
> device survives kexec.
>
> Signed-off-by: Joel Stanley <joel@....id.au>
> ---
>  drivers/usb/host/xhci.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index adc169d2fd76..ec92a843325b 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -682,6 +682,21 @@ void xhci_stop(struct usb_hcd *hcd)
>
>  	mutex_lock(&xhci->mutex);
>
> +	/*
> +	 * We can't halt the secondary HCD, because it's also the primary
> +	 * HCD, which will cause problems if we have devices attached to the
> +	 * primary HCD, like a keyboard.
> +	 */
> +	if (!usb_hcd_is_primary_hcd(hcd)) {
> +		/* The shared_hcd is going to be deallocated shortly (the USB
> +		 * core only calls this function when allocation fails in
> +		 * usb_add_hcd(), or usb_remove_hcd() is called).  So we need
> +		 * to unset xHCI's pointer.  */

    Please format this comment the same way as the comment above it.

> +		xhci->shared_hcd = NULL;
> +		mutex_unlock(&xhci->mutex);
> +		return;
> +	}
> +
>  	if (!(xhci->xhc_state & XHCI_STATE_HALTED)) {
>  		spin_lock_irq(&xhci->lock);
>
[...]

MBR, Sergei