linux-kernel - Re: [PATCH v14 3/6] usb: dwc3: Resize TX FIFOs to meet EP bursting requirements

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Date:   Tue, 20 Jul 2021 23:23:03 -0700
From:   Wesley Cheng <wcheng@...eaurora.org>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "agross@...nel.org" <agross@...nel.org>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "frowand.list@...il.com" <frowand.list@...il.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "jackp@...eaurora.org" <jackp@...eaurora.org>
Subject: Re: [PATCH v14 3/6] usb: dwc3: Resize TX FIFOs to meet EP bursting
 requirements



On 7/20/2021 4:41 AM, gregkh@...uxfoundation.org wrote:
> On Wed, Jul 14, 2021 at 12:30:07AM -0700, Wesley Cheng wrote:
>>
>>
>> On 7/13/2021 11:40 PM, Felipe Balbi wrote:
>>>
>>> Hi,
>>>
>>> Thinh Nguyen <Thinh.Nguyen@...opsys.com> writes:
>>>>> Thinh Nguyen <Thinh.Nguyen@...opsys.com> writes:
>>>>>> Wesley Cheng wrote:
>>>>>>> Some devices have USB compositions which may require multiple endpoints
>>>>>>> that support EP bursting.  HW defined TX FIFO sizes may not always be
>>>>>>> sufficient for these compositions.  By utilizing flexible TX FIFO
>>>>>>> allocation, this allows for endpoints to request the required FIFO depth to
>>>>>>> achieve higher bandwidth.  With some higher bMaxBurst configurations, using
>>>>>>> a larger TX FIFO size results in better TX throughput.
>>>>>>>
>>>>>>> By introducing the check_config() callback, the resizing logic can fetch
>>>>>>> the maximum number of endpoints used in the USB composition (can contain
>>>>>>> multiple configurations), which helps ensure that the resizing logic can
>>>>>>> fulfill the configuration(s), or return an error to the gadget layer
>>>>>>> otherwise during bind time.
>>>>>>>
>>>>>>> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
>>>>>>> ---
>>>>>>>  drivers/usb/dwc3/core.c   |  15 +++
>>>>>>>  drivers/usb/dwc3/core.h   |  16 ++++
>>>>>>>  drivers/usb/dwc3/ep0.c    |   2 +
>>>>>>>  drivers/usb/dwc3/gadget.c | 232 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>>  4 files changed, 265 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>>>>>>> index ba74ad7..b194aecd 100644
>>>>>>> --- a/drivers/usb/dwc3/core.c
>>>>>>> +++ b/drivers/usb/dwc3/core.c
>>>>>>> @@ -1267,6 +1267,7 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>>>>>>>  	u8			rx_max_burst_prd;
>>>>>>>  	u8			tx_thr_num_pkt_prd;
>>>>>>>  	u8			tx_max_burst_prd;
>>>>>>> +	u8			tx_fifo_resize_max_num;
>>>>>>>  	const char		*usb_psy_name;
>>>>>>>  	int			ret;
>>>>>>>  
>>>>>>> @@ -1282,6 +1283,13 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>>>>>>>  	 */
>>>>>>>  	hird_threshold = 12;
>>>>>>>  
>>>>>>> +	/*
>>>>>>> +	 * default to a TXFIFO size large enough to fit 6 max packets.  This
>>>>>>> +	 * allows for systems with larger bus latencies to have some headroom
>>>>>>> +	 * for endpoints that have a large bMaxBurst value.
>>>>>>> +	 */
>>>>>>> +	tx_fifo_resize_max_num = 6;
>>>>>>> +
>>>>>>>  	dwc->maximum_speed = usb_get_maximum_speed(dev);
>>>>>>>  	dwc->max_ssp_rate = usb_get_maximum_ssp_rate(dev);
>>>>>>>  	dwc->dr_mode = usb_get_dr_mode(dev);
>>>>>>> @@ -1325,6 +1333,11 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>>>>>>>  				&tx_thr_num_pkt_prd);
>>>>>>>  	device_property_read_u8(dev, "snps,tx-max-burst-prd",
>>>>>>>  				&tx_max_burst_prd);
>>>>>>> +	dwc->do_fifo_resize = device_property_read_bool(dev,
>>>>>>> +							"tx-fifo-resize");
>>>>>>> +	if (dwc->do_fifo_resize)
>>>>>>> +		device_property_read_u8(dev, "tx-fifo-max-num",
>>>>>>> +					&tx_fifo_resize_max_num);
>>>>>>
>>>>>> Why is this check here? The dwc->tx_fifo_resize_max_num should store
>>>>>> whatever property the user sets. Whether the driver wants to use this
>>>>>
>>>>> Ack!
>>>>>
>>>>>> property should depend on "dwc->do_fifo_resize". Also why don't we have
>>>>>> "snps," prefix to be consistent with the other properties?
>>>>>
>>>>> Ack!
>>>>>
>>>>>> Can we enforce to a single property? If the designer wants to enable
>>>>>> this feature, he/she can to provide the tx-fifo-max-num. This would
>>>>>> simplify the driver a bit. Since this is to optimize for performance,
>>>>>> the user should know/want/test the specific value if they want to set
>>>>>> for their setup and not hoping that the default setting not break their
>>>>>> setup. So we can remove the "do_fifo_resize" property and just check
>>>>>> whether tx_fifo_resize_max_num is set.
>>>>>
>>>>> Ack!
>>>>>
>>>>> All very valid points :-)
>>>>>
>>
>> Hi Thinh/Felipe,
>>
>>>>
>>>> Looks like this series already landed in Greg's testing branch. Not sure
>>>> how we usually handle this to address some of our concerns. Add fix
>>>> patches on top of Greg's testing branch?
>>>
>>> yup, no choice anymore :-(
>>>
>>
>> Let me review your feedback, which had some good points.  We can add a
>> change addressing everything on top of what is merged on Greg's branch.

Hi Greg,

> 
> Any hint as to when these fixups will be sent?
> 

Will get something by mid-week next week.  Sorry have been occupied with
tasks on my end.

Thanks
Wesley Cheng


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