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[91.155.214.58]) by smtp.gmail.com with ESMTPSA id d3sm15262501lfq.2.2020.05.13.00.34.50 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Wed, 13 May 2020 00:34:51 -0700 (PDT) From: Felipe Balbi To: Claus Stovgaard , Alan Stern Cc: "linux-usb\@vger.kernel.org" Subject: Re: Options for forcing dwc3 gadget to only accept superspeed In-Reply-To: <6d19d49dcfe7467556b0462b16e76677c1999875.camel@gmail.com> References: <8943a225c6d8354f2f5fe0ea7270dc0fa1293180.camel@gmail.com> <20200512195231.GA26080@rowland.harvard.edu> <6d19d49dcfe7467556b0462b16e76677c1999875.camel@gmail.com> Date: Wed, 13 May 2020 10:34:47 +0300 Message-ID: <87k11gp9t4.fsf@kernel.org> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Hi, Claus Stovgaard writes: > On tir, 2020-05-12 at 15:52 -0400, Alan Stern wrote: >> On Tue, May 12, 2020 at 09:25:38PM +0200, Claus Stovgaard wrote: >> >=20 >> > In a certain scenario I would like to force the dwc3 to only >> > connect >> > via superspeed and not fall back to USB2. >> >=20 >> > What options exist for forcing the dwc3 to keep retry? >>=20 >> The USB-3 spec forbids devices from operating only at SuperSpeed.=20=20 >> Devices must be able to connect at high speed, although possibly >> with=20 >> reduced functionality. >>=20 >> Alan Stern >>=20 > > I understand the requirement from the USB 3 specification. Though in > the scenario for this specific device, it is not about comply with the > USB 3 specification, but my question is rather what options I have for > not comply with the specification here, and then force retry of USB 3, > using the dwc3 as device. > > The device is in a fixed mounting with a fixed host. Sometimes when the > host and device is powered up, it ends in high-speed instead of super- > speed. I would like the option for "I will not be compliant with USB, > but rather retry super-speed". If it's "ending in super-speed" this means it tried RX.Detect and it failed, thus falling back to high-speed. It's likely that the signal quality in your setup has degraded or is, at least, sub-par. Forcing a SS-only setup would just give you a device that doesn't even enumerate in some cases. Could you capture dwc3 tracepoints of the problem? Also, which kernel version are you running? 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