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

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Date:   Wed, 14 Jul 2021 09:40:13 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Wesley Cheng <wcheng@...eaurora.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "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>
Cc:     "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


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 :-)
>> 
>
> 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 :-(

-- 
balbi

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