linux-kernel - Re: [PATCH v3 1/3] usb: core: hcd: Add support for deferring roothub registration

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Date:   Thu, 9 Sep 2021 12:05:28 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <chris.chiu@...onical.com>, <lokeshvutla@...com>
Subject: Re: [PATCH v3 1/3] usb: core: hcd: Add support for deferring roothub
 registration

Hi Alan,

On 08/09/21 8:21 pm, Alan Stern wrote:
> On Wed, Sep 08, 2021 at 03:23:10PM +0530, Kishon Vijay Abraham I wrote:
>> It has been observed with certain PCIe USB cards (like Inateck connected
>> to AM64 EVM or J7200 EVM) that as soon as the primary roothub is
>> registered, port status change is handled even before xHC is running
>> leading to cold plug USB devices not detected. For such cases, registering
>> both the root hubs along with the second HCD is required. Add support for
>> deferring roothub registration in usb_add_hcd(), so that both primary and
>> secondary roothubs are registered along with the second HCD.
>>
>> CC: stable@...r.kernel.org # 5.4+
>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>> Suggested-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
>> Tested-by: Chris Chiu <chris.chiu@...onical.com>
>> ---
>>  drivers/usb/core/hcd.c  | 30 ++++++++++++++++++++++++------
>>  include/linux/usb/hcd.h |  2 ++
>>  2 files changed, 26 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>> index 0f8b7c93310e..30bbf4ac4284 100644
>> --- a/drivers/usb/core/hcd.c
>> +++ b/drivers/usb/core/hcd.c
>> @@ -2775,6 +2775,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
>>  {
>>  	int retval;
>>  	struct usb_device *rhdev;
>> +	struct usb_hcd *shared_hcd;
>>  
>>  	if (!hcd->skip_phy_initialization && usb_hcd_is_primary_hcd(hcd)) {
>>  		hcd->phy_roothub = usb_phy_roothub_alloc(hcd->self.sysdev);
>> @@ -2935,13 +2936,26 @@ int usb_add_hcd(struct usb_hcd *hcd,
>>  		goto err_hcd_driver_start;
>>  	}
>>  
>> +	/* starting here, usbcore will pay attention to the shared HCD roothub */
>> +	shared_hcd = hcd->shared_hcd;
>> +	if (!usb_hcd_is_primary_hcd(hcd) && shared_hcd && HCD_DEFER_RH_REGISTER(shared_hcd)) {
>> +		retval = register_root_hub(shared_hcd);
>> +		if (retval != 0)
>> +			goto err_register_root_hub;
>> +
>> +		if (shared_hcd->uses_new_polling && HCD_POLL_RH(shared_hcd))
>> +			usb_hcd_poll_rh_status(shared_hcd);
>> +	}
>> +
>>  	/* starting here, usbcore will pay attention to this root hub */
>> -	retval = register_root_hub(hcd);
>> -	if (retval != 0)
>> -		goto err_register_root_hub;
>> +	if (!HCD_DEFER_RH_REGISTER(hcd)) {
>> +		retval = register_root_hub(hcd);
>> +		if (retval != 0)
>> +			goto err_register_root_hub;
>>  
>> -	if (hcd->uses_new_polling && HCD_POLL_RH(hcd))
>> -		usb_hcd_poll_rh_status(hcd);
>> +		if (hcd->uses_new_polling && HCD_POLL_RH(hcd))
>> +			usb_hcd_poll_rh_status(hcd);
>> +	}
>>  
>>  	return retval;
>>  
>> @@ -2985,6 +2999,7 @@ EXPORT_SYMBOL_GPL(usb_add_hcd);
>>  void usb_remove_hcd(struct usb_hcd *hcd)
>>  {
>>  	struct usb_device *rhdev = hcd->self.root_hub;
>> +	unsigned rh_registered;
> 
> This really should be a bool, not an unsigned.  (Relatively unimportant.)
> 
>>  	dev_info(hcd->self.controller, "remove, state %x\n", hcd->state);
>>  
>> @@ -2995,6 +3010,8 @@ void usb_remove_hcd(struct usb_hcd *hcd)
>>  
>>  	dev_dbg(hcd->self.controller, "roothub graceful disconnect\n");
>>  	spin_lock_irq (&hcd_root_hub_lock);
>> +	if (hcd->rh_registered == 1)
>> +		rh_registered = 1;
> 
> Just say: rh_registered = hcd->rh_registered
> 
>>  	hcd->rh_registered = 0;
>>  	spin_unlock_irq (&hcd_root_hub_lock);
>>  
>> @@ -3004,7 +3021,8 @@ void usb_remove_hcd(struct usb_hcd *hcd)
>>  	cancel_work_sync(&hcd->died_work);
>>  
>>  	mutex_lock(&usb_bus_idr_lock);
>> -	usb_disconnect(&rhdev);		/* Sets rhdev to NULL */
>> +	if (rh_registered == 1)
> 
> Just say: if (rh_registered)
> 
>> +		usb_disconnect(&rhdev);		/* Sets rhdev to NULL */
> 
> Didn't the compiler warn about using a possibly uninitialized variable?

I didn't see any. Possibly the warning levels are not correctly set in my setup.
Will address your comment and send the patch.

Thank You,
Kishon

> 
> The overall logic looks okay, apart from this one point.
> 
> Alan Stern
> 
>>  	mutex_unlock(&usb_bus_idr_lock);
>>  
>>  	/*
>> diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
>> index 548a028f2dab..2c1fc9212cf2 100644
>> --- a/include/linux/usb/hcd.h
>> +++ b/include/linux/usb/hcd.h
>> @@ -124,6 +124,7 @@ struct usb_hcd {
>>  #define HCD_FLAG_RH_RUNNING		5	/* root hub is running? */
>>  #define HCD_FLAG_DEAD			6	/* controller has died? */
>>  #define HCD_FLAG_INTF_AUTHORIZED	7	/* authorize interfaces? */
>> +#define HCD_FLAG_DEFER_RH_REGISTER	8	/* Defer roothub registration */
>>  
>>  	/* The flags can be tested using these macros; they are likely to
>>  	 * be slightly faster than test_bit().
>> @@ -134,6 +135,7 @@ struct usb_hcd {
>>  #define HCD_WAKEUP_PENDING(hcd)	((hcd)->flags & (1U << HCD_FLAG_WAKEUP_PENDING))
>>  #define HCD_RH_RUNNING(hcd)	((hcd)->flags & (1U << HCD_FLAG_RH_RUNNING))
>>  #define HCD_DEAD(hcd)		((hcd)->flags & (1U << HCD_FLAG_DEAD))
>> +#define HCD_DEFER_RH_REGISTER(hcd) ((hcd)->flags & (1U << HCD_FLAG_DEFER_RH_REGISTER))
>>  
>>  	/*
>>  	 * Specifies if interfaces are authorized by default
>> -- 
>> 2.17.1
>>