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 08:52:41 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Wesley Cheng <wcheng@...eaurora.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>,
        "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 Wed, Jul 14, 2021 at 09:40:13AM +0300, 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 :-)
> >> 
> >
> > 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 :-(

I took these as they seemed correct.  If they need to be reverted,
that's fine I can do that.  But it looks like Wesley can just make some
simple changes on top of them to resolve the remaining issues, right?

thanks,

greg k-h