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[83.28.84.190]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-472c7bec9c2sm7927088f8f.12.2026.06.28.10.22.06 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Sun, 28 Jun 2026 10:22:07 -0700 (PDT) Date: Sun, 28 Jun 2026 19:22:03 +0200 From: Michal Pecio To: Alan Stern Cc: Nikhil Solanke , linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v2] usbcore: Add quirk for 255-bytes initial config read Message-ID: <20260628192203.5fb9daac.michal.pecio@gmail.com> In-Reply-To: <20260628190201.00afdccf.michal.pecio@gmail.com> References: <20260623161035.5792-1-nikhilsolanke5@gmail.com> <567e8866-4308-4e5f-819c-fe778dbf74f8@rowland.harvard.edu> <5159fd69-dddf-4073-a8e7-95fa77de0b7f@rowland.harvard.edu> <02060df3-b8c5-4a86-b3ab-3a28eea8a562@rowland.harvard.edu> <20260628165040.76fd608d.michal.pecio@gmail.com> <62e1fab3-1045-41f3-bc74-4c7624011619@rowland.harvard.edu> <20260628190201.00afdccf.michal.pecio@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit I really think it could (and should) be a simple patch. This is what I wrote a few weeks ago. It's an unconditional change for all devices, but it would be easy to turn it into a quirk. --- a/drivers/usb/core/config.c +++ b/drivers/usb/core/config.c @@ -938,15 +938,14 @@ int usb_get_configuration(struct usb_device *dev) if (!dev->rawdescriptors) return -ENOMEM; - desc = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL); + desc = kmalloc(255, GFP_KERNEL); if (!desc) return -ENOMEM; for (cfgno = 0; cfgno < ncfg; cfgno++) { - /* We grab just the first descriptor so we know how long - * the whole configuration is */ + /* Try 255 bytes first because that's what Windows does */ result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno, - desc, USB_DT_CONFIG_SIZE); + desc, 255); if (result < 0) { dev_err(ddev, "unable to read config index %d " "descriptor/%s: %d\n", cfgno, "start", result); @@ -975,8 +974,12 @@ int usb_get_configuration(struct usb_device *dev) if (dev->quirks & USB_QUIRK_DELAY_INIT) msleep(200); - result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno, - bigbuffer, length); + /* Don't bother if we already have it all */ + if (length <= result) + memcpy(bigbuffer, desc, length); + else + result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno, + bigbuffer, length); if (result < 0) { dev_err(ddev, "unable to read config index %d " "descriptor/%s\n", cfgno, "all");