linux-kernel - Re: [RFC PATCH 06/14] usb: core: hcd: Introduce USB HCD APIs for interrupter management

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Date:   Tue, 27 Dec 2022 13:07:45 -0800
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
        <perex@...ex.cz>, <broonie@...nel.org>, <lgirdwood@...il.com>,
        <andersson@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <gregkh@...uxfoundation.org>, <Thinh.Nguyen@...opsys.com>,
        <bgoswami@...cinc.com>, <tiwai@...e.com>, <robh+dt@...nel.org>,
        <agross@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <devicetree@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <quic_jackp@...cinc.com>, <quic_plai@...cinc.com>
Subject: Re: [RFC PATCH 06/14] usb: core: hcd: Introduce USB HCD APIs for
 interrupter management

Hi Alan,

On 12/24/2022 7:29 AM, Alan Stern wrote:
> On Fri, Dec 23, 2022 at 03:31:52PM -0800, Wesley Cheng wrote:
>> For USB HCDs that can support multiple USB interrupters, expose functions
>> that class drivers can utilize for setting up secondary interrupters.
>> Class drivers can pass this information to its respective clients, i.e.
>> a dedicated DSP.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> ---
>>   drivers/usb/core/hcd.c  | 86 +++++++++++++++++++++++++++++++++++++++++
>>   include/linux/usb.h     |  7 ++++
>>   include/linux/usb/hcd.h | 16 +++++++-
>>   3 files changed, 108 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>> index 8300baedafd2..90ead90faf1d 100644
>> --- a/drivers/usb/core/hcd.c
>> +++ b/drivers/usb/core/hcd.c
> 
>> +/**
>> + * usb_hcd_stop_endpoint - Halt USB EP transfers
>> + * @udev: usb device
>> + * @ep: usb ep to stop
>> + *
>> + * Stop pending transfers on a specific USB endpoint.
>> + **/
>> +int usb_hcd_stop_endpoint(struct usb_device *udev,
>> +					struct usb_host_endpoint *ep)
>> +{
>> +	struct usb_hcd *hcd = bus_to_hcd(udev->bus);
>> +	int ret = 0;
>> +
>> +	if (hcd->driver->stop_endpoint)
>> +		ret = hcd->driver->stop_endpoint(hcd, udev, ep);
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(usb_hcd_stop_endpoint);
> 
> You know, there already is a function that does this.  It's named
> usb_hcd_flush_endpoint().  No need to add another function that does the
> same thing.
> 

Thanks for the suggestion and review.

Hmmm...maybe I should change the name of the API then to avoid the 
confusion.  Yes, usb_hcd_flush_endpoint() does ensure that URBs 
submitted to the EP are stopped.  However, with this offloading concept, 
we aren't actually submitting URBs from the main processor, so the 
ep->urb_list will be empty.

This means the usb_hcd_flush_endpoint() API won't actually do anything. 
  What we need is to ensure that we send a XHCI stop ep command to the 
controller.

Thanks
Wesley Cheng