[PATCH 3/4] configs: Increase USB Hub debounce timeout in Agilex5

[Marek Vasut]

On 9/8/25 3:41 PM, Ravulapalli, Naresh Kumar wrote:
> 
> 
> On 08-Sep-25 6:32 PM, Marek Vasut wrote:
>>
>> On 9/8/25 10:44 AM, Ravulapalli, Naresh Kumar wrote:
>>> Hi Marek
>>>
>>> On 02-Sep-25 11:48 PM, Marek Vasut wrote:
>>>> [CAUTION: This email is from outside your organization. Unless you
>>>> trust the sender, do not click on links or open attachments as it may
>>>> be a fraudulent email attempting to steal your information and/or
>>>> compromise your computer.]
>>>>
>>>> On 9/2/25 9:52 AM, Ravulapalli, Naresh Kumar wrote:
>>>>>
>>>>>
>>>>> On 30-Aug-25 5:30 AM, Marek Vasut wrote:
>>>>>>
>>>>>> On 8/29/25 6:19 PM, Ravulapalli, Naresh Kumar wrote:
>>>>>>> Hi Marek
>>>>>>>
>>>>>>> On 29-Aug-25 2:11 PM, Marek Vasut wrote:
>>>>>>>>
>>>>>>>> On 8/8/25 12:04 PM, Naresh Kumar Ravulapalli wrote:
>>>>>>>>> Some USB devices need more time to be initialized. Hence,
>>>>>>>>> increasing the default USB Hub debounce timeout value for
>>>>>>>>> devices to be discovered, connected to Agilex5 boards.
>>>>>>>> Is this really hub debounce timeout or usb_pgood_delay ?
>>>>>>>>
>>>>>>>> Which devices are those, include that in the commit message.
>>>>>>>
>>>>>>> Yes, timeout is related to USB connect/disconnect signal bounces not
>>>>>>> about bus stability during init.
>>>>>>>
>>>>>>> Issue was mainly observed with legacy flash drives. Maybe I will
>>>>>>> change
>>>>>>> commit text from "Some USB devices need more time to be
>>>>>>> initialized..."
>>>>>>> to "Some old USB flash drives need more time to be initialized 
>>>>>>> during
>>>>>>> connect or disconnect events ..."?
>>>>>>>
>>>>>>> Note that I am not modifying the default Kconfig value in general;
>>>>>>> change is only made for an SoCFPGA devkit we tested.
>>>>>> Does this same issue go away if you set usb_pgood_delay to 2000 or
>>>>>> higher too ?
>>>>>
>>>>> No, changing USB HUB debounce timeout is working for us.
>>>> Look at this code:
>>>>
>>>> https://source.denx.de/u-boot/u-boot/-/blob/master/common/usb_hub.c?
>>>> ref_type=heads#L199
>>>>
>>>> "
>>>> #if CONFIG_IS_ENABLED(ENV_SUPPORT)
>>>>         env = env_get("usb_pgood_delay");
>>>>         if (env)
>>>>                 pgood_delay = max(pgood_delay,
>>>>                                   (unsigned)simple_strtol(env, NULL, 
>>>> 0));
>>>> #endif
>>>>         debug("pgood_delay=%dms\n", pgood_delay);
>>>>
>>>>         /*
>>>>          * Do a minimum delay of the larger value of 100ms or 
>>>> pgood_delay
>>>>          * so that the power can stablize before the devices are 
>>>> queried
>>>>          */
>>>>         hub->query_delay = get_timer(0) + max(100, (int)pgood_delay);
>>>>
>>>>         /*
>>>>          * Record the power-on timeout here. The max. delay (timeout)
>>>>          * will be done based on this value in the USB port loop in
>>>>          * usb_hub_configure() later.
>>>>          */
>>>>         hub->connect_timeout = hub->query_delay + HUB_DEBOUNCE_TIMEOUT;
>>>>         debug("devnum=%d poweron: query_delay=%d connect_timeout=%d\n",
>>>>               dev->devnum, max(100, (int)pgood_delay),
>>>>               max(100, (int)pgood_delay) + HUB_DEBOUNCE_TIMEOUT);
>>>> "
>>>>
>>>> Changing both usb_pgood_delay or (CONFIG_USB_)HUB_DEBOUNCE_TIMEOUT
>>>> should have the same effect. How come it does not ?
>>>
>>> CONFIG_USB_HUB_DEBOUNCE_TIMEOUT and pgood_delay are used for different
>>> purposes. If I am not mistaken I think I explained this in my earlier
>>> comments.
>>>
>>> Anyway, to further elaborate, CONFIG_USB_HUB_DEBOUNCE_TIMEOUT is used
>>> for debounce timeouts during device connect events and pgood_delay is
>>> used during initial VBus stabilization.
>>>
>>> You would be able to see this difference in the link below, where
>>> pgood_delay which is populated into "hub->query_delay" is used for
>>> voltages to stabilize before initiating communication and "hub-
>>>  >connect_timeout" where "HUB_DEBOUNCE_TIMEOUT" is populated is used
>>> after getting the port status.
>>>
>>> https://github.com/u-boot/u-boot/ 
>>> blob/328747974a0620d0996113fe2b3906b06e96de00/common/usb_hub.c#L455
>>>
>>> Also, the change made as part of the comment is not applicable to the
>>> USB stack in general; it is only for our devkit defconfig.
>> But none of this answers my question, looking at the aforementioned code
>> -- Changing both usb_pgood_delay or (CONFIG_USB_)HUB_DEBOUNCE_TIMEOUT
>> should have the same effect. How come it does not in your case ?
> 
> Maybe I wasn't explicit in my earlier comment, "No, changing USB HUB 
> debounce timeout is working for us."

USB_HUB_DEBOUNCE_TIMEOUT is basically the hard-coded-into-U-Boot-binary 
version of "usb_pgood_delay" . The upside of "usb_pgood_delay" is that 
users can change the value at runtime, which helps in case users need to 
use some broken USB storage device which takes more than 
"usb_pgood_delay" ms to start up. You cannot do that with 
USB_HUB_DEBOUNCE_TIMEOUT .

Since the commit description talks about "Some USB devices need more 
time to be initialized." , this looks more like "usb_pgood_delay" type 
of issue.

> What I meant is I didn't want to modify usb_pgood_delay as my issue was 
> with HUB_DEBOUNCE_TIMEOUT, so modifying this value worked for us.

Does it also work if you modify usb_pgood_delay instead ?