Re: [PATCH v5 09/12] xhci: introduce xhci->lost_power flag

[Roger Quadros <rogerq@kernel.org>]

On 26/07/2024 21:17, Théo Lebrun wrote:
> The XHCI_RESET_ON_RESUME quirk allows wrappers to signal that they
> expect a reset after resume. It is also used by some to enforce a XHCI
> reset on resume (see needs-reset-on-resume DT prop).
> 
> Some wrappers are unsure beforehands if they will reset. Add a mechanism
> to signal *at resume* if power has been lost. Parent devices can set
> this flag, that defaults to the XHCI_RESET_ON_RESUME value.
> 
> The XHCI_RESET_ON_RESUME quirk still triggers a runtime_pm_get() on the
> controller. This is required as we do not know if a suspend will
> trigger a reset, so the best guess is to avoid runtime PM.
> 
> Reset the xhci->lost_power value each time in xhci_resume(), making it
> safe for devices to only set lost_power on some resumes.
> 
> Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
> ---
>  drivers/usb/host/xhci.c | 8 +++++++-
>  drivers/usb/host/xhci.h | 6 ++++++
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index 0a8cf6c17f82..2c9b32d339f9 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -1029,9 +1029,12 @@ int xhci_resume(struct xhci_hcd *xhci, pm_message_t msg)
>  
>  	spin_lock_irq(&xhci->lock);
>  
> -	if (hibernated || xhci->quirks & XHCI_RESET_ON_RESUME || xhci->broken_suspend)
> +	if (hibernated || xhci->lost_power || xhci->broken_suspend)

Why not treat xhci->lost_power and xhci->quriks & XHCI_RESET_ON_RESUME independently?

XHCI_RESET_ON_RESUME is sued by devices that know they always need to be reset on resume.

xhci->lost_power is used by devices that don't have consistent behavior.


>  		reinit_xhc = true;
>  
> +	/* Reset to default value, parent devices might correct it at next resume. */
> +	xhci->lost_power = !!(xhci->quirks & XHCI_RESET_ON_RESUME);
> +

then you don't need to do this.

>  	if (!reinit_xhc) {
>  		/*
>  		 * Some controllers might lose power during suspend, so wait
> @@ -5228,6 +5231,9 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
>  	if (get_quirks)
>  		get_quirks(dev, xhci);
>  
> +	/* Default value, that can be corrected at resume. */
> +	xhci->lost_power = !!(xhci->quirks & XHCI_RESET_ON_RESUME);
> + 

nor this.

>  	/* In xhci controllers which follow xhci 1.0 spec gives a spurious
>  	 * success event after a short transfer. This quirk will ignore such
>  	 * spurious event.
> diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
> index ebd0afd59a60..ec7c6061363f 100644
> --- a/drivers/usb/host/xhci.h
> +++ b/drivers/usb/host/xhci.h
> @@ -1640,6 +1640,12 @@ struct xhci_hcd {
>  	unsigned		broken_suspend:1;
>  	/* Indicates that omitting hcd is supported if root hub has no ports */
>  	unsigned		allow_single_roothub:1;
> +	/*
> +	 * Signal from upper stacks that we lost power during system-wide
> +	 * suspend. Its default value is based on XHCI_RESET_ON_RESUME, meaning
> +	 * it is safe for wrappers to not modify lost_power at resume.
> +	 */
> +	unsigned                lost_power:1;
>  	/* cached extended protocol port capabilities */
>  	struct xhci_port_cap	*port_caps;
>  	unsigned int		num_port_caps;
> 

-- 
cheers,
-roger