linux-kernel - Re: [PATCH v6 3/4] usb: dwc3: Resize TX FIFOs to meet EP bursting requirements

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Message-ID: <YA+lVFWlBDvN4MTF@builder.lan>
Date:   Mon, 25 Jan 2021 23:15:00 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Wesley Cheng <wcheng@...eaurora.org>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org, robh+dt@...nel.org,
        agross@...nel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, peter.chen@....com,
        jackp@...eaurora.org
Subject: Re: [PATCH v6 3/4] usb: dwc3: Resize TX FIFOs to meet EP bursting
 requirements

On Mon 25 Jan 22:32 CST 2021, Wesley Cheng wrote:
> On 1/25/2021 5:55 PM, Bjorn Andersson wrote:
> > On Mon 25 Jan 19:14 CST 2021, Wesley Cheng wrote:
> > 
> >>
> >>
> >> On 1/22/2021 9:12 AM, Bjorn Andersson wrote:
> >>> On Thu 21 Jan 22:01 CST 2021, Wesley Cheng wrote:
> >>>
> >>
> >> Hi Bjorn,
> >>>
> >>> Under what circumstances should we specify this? And in particular are
> >>> there scenarios (in the Qualcomm platforms) where this must not be set?
> >>> The TXFIFO dynamic allocation is actually a feature within the DWC3
> >> controller, and isn't specifically for QCOM based platforms.  It won't
> >> do any harm functionally if this flag is not set, as this is meant for
> >> enhancing performance/bandwidth.
> >>
> >>> In particular, the composition can be changed in runtime, so should we
> >>> set this for all Qualcomm platforms?
> >>>
> >> Ideally yes, if we want to increase bandwith for situations where SS
> >> endpoint bursting is set to a higher value.
> >>
> >>> And if that's the case, can we not just set it from the qcom driver?
> >>>
> >> Since this is a common DWC3 core feature, I think it would make more
> >> sense to have it in DWC3 core instead of a vendor's DWC3 glue driver.
> >>
> > 
> > I don't have any objections to implementing it in the core driver, but
> > my question is can we just skip the DT binding and just enable it from
> > the vendor driver?
> > 
> > Regards,
> > Bjorn
> > 
> 
> Hi Bjorn,
> 
> I see.  I think there are some designs which don't have a DWC3 glue
> driver, so assuming there may be other platforms using this, there may
> not always be a vendor driver to set this.
> 

You mean that there are implementations of dwc3 without an associated
glue driver that haven't yet realized that they need this feature?

I would suggest then that we implement the core code necessary, we
enable it from the Qualcomm glue layer and when someone realize that
they need this without a glue driver it's going to be trivial to add the
DT binding.


The alternative is that we're lugging around a requirement to specify
this property in all past, present and future Qualcomm dts files - and
then we'll need to hard code it for ACPI anyways.

Regards,
Bjorn