Re: [RFC PATCH] usb: core: reduce power-on-good delay time of root hub

[Alan Stern]

On Fri, Apr 09, 2021 at 10:39:07AM +0800, Chunfeng Yun wrote:
> Return the exactly delay time given by root hub descriptor,
> this helps to reduce resume time etc.
> 
> Due to the root hub descriptor is usually provided by the host
> controller driver, if there is compatibility for a root hub,
> we can fix it easily without affect other root hub
> 
> Signed-off-by: Chunfeng Yun 

Acked-by: Alan Stern 

> ---
>  drivers/usb/core/hub.h | 6 --
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
> index 73f4482d833a..22ea1f4f2d66 100644
> --- a/drivers/usb/core/hub.h
> +++ b/drivers/usb/core/hub.h
> @@ -148,8 +148,10 @@ static inline unsigned hub_power_on_good_delay(struct 
> usb_hub *hub)
>  {
>   unsigned delay = hub->descriptor->bPwrOn2PwrGood * 2;
>  
> - /* Wait at least 100 msec for power to become stable */
> - return max(delay, 100U);
> + if (!hub->hdev->parent) /* root hub */
> + return delay;
> + else /* Wait at least 100 msec for power to become stable */
> + return max(delay, 100U);
>  }
>  
>  static inline int hub_port_debounce_be_connected(struct usb_hub *hub,
> -- 
> 2.18.0
> 

[RFC PATCH] usb: core: reduce power-on-good delay time of root hub

[Chunfeng Yun]

Return the exactly delay time given by root hub descriptor,
this helps to reduce resume time etc.

Due to the root hub descriptor is usually provided by the host
controller driver, if there is compatibility for a root hub,
we can fix it easily without affect other root hub

Signed-off-by: Chunfeng Yun 
---
 drivers/usb/core/hub.h | 6 --
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
index 73f4482d833a..22ea1f4f2d66 100644
--- a/drivers/usb/core/hub.h
+++ b/drivers/usb/core/hub.h
@@ -148,8 +148,10 @@ static inline unsigned hub_power_on_good_delay(struct 
usb_hub *hub)
 {
unsigned delay = hub->descriptor->bPwrOn2PwrGood * 2;
 
-   /* Wait at least 100 msec for power to become stable */
-   return max(delay, 100U);
+   if (!hub->hdev->parent) /* root hub */
+   return delay;
+   else /* Wait at least 100 msec for power to become stable */
+   return max(delay, 100U);
 }
 
 static inline int hub_port_debounce_be_connected(struct usb_hub *hub,
-- 
2.18.0