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[2a01:c23:614a:dd00:5305:d3a4:b23:147e]) by smtp.gmail.com with ESMTPSA id bw4-20020a170906c1c400b00992e94bcfabsm3088615ejb.167.2023.11.05.07.33.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Nov 2023 07:33:02 -0800 (PST) Date: Sun, 5 Nov 2023 16:33:00 +0100 From: Fabian Melzow To: Alan Stern Cc: linux-usb@vger.kernel.org Subject: Re: 0bda:b812 USB "3.0" WLAN devices only report a maximum of 480 Mbps Message-ID: <20231105163300.3b8df5ad@ping> In-Reply-To: <76fc65db-4efe-4da7-a13f-d7a451f836fa@rowland.harvard.edu> References: <20231105130215.2b669c8b@ping> <2023110540-unseemly-mobilize-9e82@gregkh> <20231105134909.6c3f28d1@ping> <2023110534-fester-schematic-818a@gregkh> <20231105143051.2b28c316@ping> <76fc65db-4efe-4da7-a13f-d7a451f836fa@rowland.harvard.edu> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Am Sun, 5 Nov 2023 09:56:06 -0500 schrieb Alan Stern : > On Sun, Nov 05, 2023 at 02:30:51PM +0100, Fabian Melzow wrote: > > Am Sun, 5 Nov 2023 14:11:02 +0100 > > schrieb Greg KH : > > > > > On Sun, Nov 05, 2023 at 01:49:09PM +0100, Fabian Melzow wrote: > > > > Am Sun, 5 Nov 2023 13:20:38 +0100 > > > > schrieb Greg KH : > > > > > > > > > On Sun, Nov 05, 2023 at 01:02:15PM +0100, Fabian Melzow > > > > > wrote: > > > > > > These devices should report 5 Gbps for USB 3.0 in the Binary > > > > > > Object Store Descriptor, but don't do so. > > > > > > > > > > Why do you think these should report 5 Gbps? If the device > > > > > descriptor does not show it, there's nothing that we can do > > > > > about it in the operating system, sorry. > > > > > > > > Thanks. I don't look at the USB specification for USB >2.0, > > > > which was long times ago and then only for a user space program > > > > and thought that it at least theoretically could be possible to > > > > set the device speed at some kind of initialization. > > > > > > There might be some vendor-specific way of doing this, and then > > > the device resets itself, but other than that, no, descriptors > > > are a static description of the device's capabilities. > > > > When this static description is also used by the host controller to > > set the device speed, then these WLAN devices are limited to 480 > > Mbps. If > > The speed is not set by the host controller; it is set by the device. > > If the device is capable of running at a higher speed than 480 Mbps > then it should do so. Have you checked the actual connection speed, > as reported in the "speed" file in the device's sysfs directory or in > the output from "lsusb -t"? $ lsusb -t (only relevant output) /: Bus 001.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/14p, 480M |__ Port 004: Dev 003, If 0, Class=Vendor Specific Class, Driver=rtw_8822bu, 480M > > How do you know that the device's USB hardware supports more than 480 > Mbps? And even if the hardware does, maybe the firmware doesn't. > > (Note: Just because the device's WLAN interface can run at 780 Mbps, > it does not follow that the USB interface can run that fast.) These USB WLAN sticks are sold as "USB 3.0", and also have a blue USB-3.0-A-plug. I don't really know the speed, but 480 Mbps is reported by "lsusb -t" or in the descriptor. I did not open these devices, but have assumed that they only use a single chip to handle everything, WLAN and USB. > > > > > What exactly is the hardware problem? What is not working > > > > > "properly" for them? > > > > > > > > All 0bda:b812 USB-WLAN-devices seems to only operate at 480 > > > > Mbps, but have a WLAN-chip which supports 780 Mbps at maximum. > > > > > > > > > > Are you sure that those devices really can run at 480 Mbps? > > > Perhaps the chip can support higher, but the firmware on the > > > device, and the other stuff in the device does not? > > > > The used WLAN chipset should support more then 480 Mbps in hardware, > > but I don't known whether the host controller limits the speed > > based on the wrong descriptor of the device. > > The speed is not determined by the device's descriptors; it is > negotiated at the hardware level between the device and the upstream > hub when the USB port is reset, which happens shortly after the > device is plugged in, as part of initialization. > > Another thing to watch out for: Even a 10-Gbps-capable device will be > forced to run at a measly 480 Mbps if it is connected via a USB-2 > cable rather than a USB-3 cable. The above lsusb-output, is from plugging the stick direct into a 10 Gbps-USB 3.1-A-port, with it's A-plug in the case.