From:   Yaqin Pan <akingchen@vivo.com>
To:     gregkh@linuxfoundation.org
Cc:     akingchen@vivo.com, balbi@kernel.org, devicetree@vger.kernel.org,
        kernel@vivo.com, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org, robh+dt@kernel.org
Subject: Re: [PATCH v3 1/2] usb: dwc3: Add a quirk to set GUCTL.SPRSCTRLTRANSEN bit.
Date:   Thu, 30 Dec 2021 23:36:12 +0800
Message-Id: <20211230153612.15063-1-akingchen@vivo.com>
In-Reply-To: <Yc2+S6u++cXYAnkt@kroah.com>
References: <Yc2+S6u++cXYAnkt@kroah.com>
Precedence: bulk

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.