From nobody Thu Apr 9 14:59:18 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4AF76395D8F for ; Mon, 2 Mar 2026 10:28:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772447319; cv=none; b=g9MlkVGP/R8toca4m2h6K+vhVibK9Q3f/Q/KmopuX9aaVd7kJhv9ftIyLyhK56GOnRpQGcKV1Bv7meHR/6+i01LAKXK73n+HfGRg9VbKwdLBRFf/hBotZaV7QyPcDnxZmKXGLgTKwf1H+LXE7HN2UEy2YEkmyqRSSAymbF5A8vQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772447319; c=relaxed/simple; bh=3Ek4YwwN0iALLUmx6aIRwN9VWVamLWFry2CPHmZdgR0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=dXIsUoEy1jRIrlD4jrPiPan32zb+2xUUZHvwpMq0uIHLN7c8aiiGuQl+0yKxXd8lFrqQRRHxhimjvXXkTJoV9vQOR4r4dmgDOtwCGAj8YhfzU2uGXGucMFk6I+noIamYv+sdU7CuIAoCJAiLbtCmVyEbfRQnPMD/UUCVrbyWDeE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=JQzrLZK7; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JQzrLZK7" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772447317; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=hvw7wOLhNfMOHZ6J4wCB8Ewfi6ITUfrSGx/wZCr55HM=; b=JQzrLZK75LdriYE9cEp2+afqZVRvwVkiNUc9O8tcOEpQRDbDOGiTKkG4PIqB63f8Gwhgbw dBnYPCI6l8nelnd6JF4Oh1vceRUt/fJRFVMKod07niQrH0s7e9TtD09yUcPya3pzXoBen1 y8Zj98WvJBLlahDI+NVObMjZNgFdrNg= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-685-T1xHSYiONteNIYVSDCg0Hg-1; Mon, 02 Mar 2026 05:28:31 -0500 X-MC-Unique: T1xHSYiONteNIYVSDCg0Hg-1 X-Mimecast-MFC-AGG-ID: T1xHSYiONteNIYVSDCg0Hg_1772447310 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 09B461800451; Mon, 2 Mar 2026 10:28:30 +0000 (UTC) Received: from lenovo-t14s.redhat.com (unknown [10.45.224.171]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 806981800296; Mon, 2 Mar 2026 10:28:27 +0000 (UTC) From: Laurent Vivier To: Jakub Kicinski Cc: linux-kernel@vger.kernel.org, Daniele Palmas , Stefano Brivio , Koen Vandeputte , linux-usb@vger.kernel.org, netdev@vger.kernel.org, Laurent Vivier Subject: [PATCH] qmi_wwan: allow max_mtu above hard_mtu to control rx_urb_size Date: Mon, 2 Mar 2026 11:28:25 +0100 Message-ID: <20260302102825.274385-1-lvivier@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Content-Type: text/plain; charset="utf-8" Commit c7159e960f14 ("usbnet: limit max_mtu based on device's hard_mtu") capped net->max_mtu to the device's hard_mtu in usbnet_probe(). While this correctly prevents oversized packets on standard USB network devices, it breaks the qmi_wwan driver. qmi_wwan relies on userspace (e.g. ModemManager) setting a large MTU on the wwan0 interface to configure rx_urb_size via usbnet_change_mtu(). QMI modems negotiate USB transfer sizes of 16,383 or 32,767 bytes, and the USB receive buffers must be sized accordingly. With max_mtu capped to hard_mtu (~1500 bytes), userspace can no longer raise the MTU, the receive buffers remain small, and download speeds drop from >300 Mbps to ~0.8 Mbps. Introduce a FLAG_NOMAXMTU driver flag that allows individual usbnet drivers to opt out of the max_mtu cap. Set this flag in qmi_wwan's driver_info structures to restore the previous behavior for QMI devices, while keeping the safety fix in place for all other usbnet drivers. Fixes: c7159e960f14 ("usbnet: limit max_mtu based on device's hard_mtu") Reported-by: Koen Vandeputte Tested-by: Daniele Palmas Signed-off-by: Laurent Vivier --- drivers/net/usb/qmi_wwan.c | 4 ++-- drivers/net/usb/usbnet.c | 7 ++++--- include/linux/usb/usbnet.h | 1 + 3 files changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c index 3a4985b582cb..05acac10cd2b 100644 --- a/drivers/net/usb/qmi_wwan.c +++ b/drivers/net/usb/qmi_wwan.c @@ -928,7 +928,7 @@ static int qmi_wwan_resume(struct usb_interface *intf) =20 static const struct driver_info qmi_wwan_info =3D { .description =3D "WWAN/QMI device", - .flags =3D FLAG_WWAN | FLAG_SEND_ZLP, + .flags =3D FLAG_WWAN | FLAG_NOMAXMTU | FLAG_SEND_ZLP, .bind =3D qmi_wwan_bind, .unbind =3D qmi_wwan_unbind, .manage_power =3D qmi_wwan_manage_power, @@ -937,7 +937,7 @@ static const struct driver_info qmi_wwan_info =3D { =20 static const struct driver_info qmi_wwan_info_quirk_dtr =3D { .description =3D "WWAN/QMI device", - .flags =3D FLAG_WWAN | FLAG_SEND_ZLP, + .flags =3D FLAG_WWAN | FLAG_NOMAXMTU | FLAG_SEND_ZLP, .bind =3D qmi_wwan_bind, .unbind =3D qmi_wwan_unbind, .manage_power =3D qmi_wwan_manage_power, diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index ed86ba87ca4e..b72ba0803392 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1829,11 +1829,12 @@ usbnet_probe(struct usb_interface *udev, const stru= ct usb_device_id *prod) if ((dev->driver_info->flags & FLAG_NOARP) !=3D 0) net->flags |=3D IFF_NOARP; =20 - if (net->max_mtu > (dev->hard_mtu - net->hard_header_len)) + if ((dev->driver_info->flags & FLAG_NOMAXMTU) =3D=3D 0 && + net->max_mtu > (dev->hard_mtu - net->hard_header_len)) net->max_mtu =3D dev->hard_mtu - net->hard_header_len; =20 - if (net->mtu > net->max_mtu) - net->mtu =3D net->max_mtu; + if (net->mtu > (dev->hard_mtu - net->hard_header_len)) + net->mtu =3D dev->hard_mtu - net->hard_header_len; =20 } else if (!info->in || !info->out) status =3D usbnet_get_endpoints(dev, udev); diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h index b0e84896e6ac..bbf799ccf3b3 100644 --- a/include/linux/usb/usbnet.h +++ b/include/linux/usb/usbnet.h @@ -132,6 +132,7 @@ struct driver_info { #define FLAG_MULTI_PACKET 0x2000 #define FLAG_RX_ASSEMBLE 0x4000 /* rx packets may span >1 frames */ #define FLAG_NOARP 0x8000 /* device can't do ARP */ +#define FLAG_NOMAXMTU 0x10000 /* allow max_mtu above hard_mtu */ =20 /* init device ... can sleep, or cause probe() failure */ int (*bind)(struct usbnet *, struct usb_interface *); --=20 2.53.0