linux-kernel - Re: [PATCH v3 1/2] usb: dwc3: Add a quirk to set GUCTL.SPRSCTRLTRANSEN bit.

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Date:   Thu, 30 Dec 2021 16:48:09 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yaqin Pan <akingchen@...o.com>
Cc:     balbi@...nel.org, devicetree@...r.kernel.org, kernel@...o.com,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        robh+dt@...nel.org
Subject: Re: [PATCH v3 1/2] usb: dwc3: Add a quirk to set
 GUCTL.SPRSCTRLTRANSEN bit.

On Thu, Dec 30, 2021 at 11:36:12PM +0800, Yaqin Pan wrote:
> On Thu, 30 Dec 2021 15:12:27 +0100 Greg Kroah-Hartman wrote:
> >> This quirk is only for dwc3 host mode.
> >> the dwc3 controller can't emurate some devices successfully.
> >> For example, TF card reader (aaaa:8816):
> >> failed log
> >> usb 1-1: new high-speed USB device number 2 using xhci-hcd
> >> usb 1-1: device descriptor read/all, error -110
> >> >From the usb analyzer, always return NAK in the data phase.
> >> if enable the GUCTL.SPRSCTRLTRANSEN bit. then the log is:
> >> usb 2-1: new high-speed USB device number 3 using xhci-hcd
> >> usb 2-1: New USB device found, idVendor=aaaa,
> >> idProduct=8816, bcdDevice=13.08
> >> usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
> >> usb 2-1: Product: MXT USB Device
> >> usb 2-1: Manufacturer: MXTronics
> >> usb 2-1: SerialNumber: 150101v01
> >> usb 2-1: New USB device found, VID=aaaa, PID=8816
> >> 
> >> Some devices are slow in responding to Control transfers.
> >> Scheduling mulitiple transactions in one microframe/frame
> >> can cause the devices to misbehave. if this qurik is enabled,
> >> the host controller schedules transations for a Control transfer
> >> in defferent microframes/frame.
> >
> >If this is needed for all devices (i.e. you do not know what device is
> >going to be plugged in), why not just enable it for all controllers?
> >Why whould you NOT want this enabled?
> >
> >Or is this a broken hardware device and only specific host controllers
> >need this?  If so, how do we know which ones need this set and which do
> >not?
> 
> I think not all dwc3 controllers need this. For cell phone,customers may
> use various usb devices, we can enable this quirk to fix some compatibility
> issues. For some chip platform of qcom, i encounter this issue, not every
> platform i encounter this problem.
> 
> If enabled for all controllers, it will reduce the speed of Control transfers. 
> So i think it would be better for user to enable it by their own purposes.

But how do hardware vendors know to enable this?  Can we trigger off of
PCI ids?  Do we need a list of quirks to show which host controllers are
broken this way?

Burying something as basic as "reliable device connection" in a DT quirk
seems very sloppy to me.  We want reliable systems, right?

thanks,

greg k-h