From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-m49206.qiye.163.com (mail-m49206.qiye.163.com [45.254.49.206]) (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 96A8F29B793; Mon, 25 Aug 2025 08:11:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.254.49.206 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756109482; cv=none; b=hAJTQtGhcHUXZ+d0epsJZ5P2gPLWcunKgQumYhwNc/VQ+U6PZIM31DASQj9ljNj4Xv+18+5RQqKOwGOtMd1BUrg6Y8YU6Ct5u/k/NPg5oMjVkW04I+MljMdPg8p5mogZVgzLMNhmcm2xWBkwakag6piRFFKGpkSOSmPGY4NHSAM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756109482; c=relaxed/simple; bh=NGv79DTk6F7a87cvl4FUlWH3mVBfPqdnx9mJIeeHa5c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Rjw2y891k4GLhCthBeJ3KWvpzrT3tItSjBrQ/5esRl3vTfHBBIHDYUCVSVpXEjAxnO2YF8BxwD1B5j6lkLudgAJ9ycBj58RNtHjT69aG6K9OH6j8UzGHjwyeANFYy3mFB9urd955JcuO5x7ZqakGhCVTvbAyiw8s07YV3UQn0y8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rock-chips.com; spf=pass smtp.mailfrom=rock-chips.com; dkim=pass (1024-bit key) header.d=rock-chips.com header.i=@rock-chips.com header.b=jZTcCQqM; arc=none smtp.client-ip=45.254.49.206 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rock-chips.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=rock-chips.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=rock-chips.com header.i=@rock-chips.com header.b="jZTcCQqM" Received: from [172.16.33.94] (unknown [58.22.7.114]) by smtp.qiye.163.com (Hmail) with ESMTP id 20740ab50; Mon, 25 Aug 2025 11:35:11 +0800 (GMT+08:00) Message-ID: <5252b43d-a7ee-42b5-932e-6c6eadd04543@rock-chips.com> Date: Mon, 25 Aug 2025 11:35:10 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] usb: gadget: f_hid: Fix zero length packet transfer To: Alan Stern Cc: gregkh@linuxfoundation.org, Chris.Wulff@biamp.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, frank.wang@rock-chips.com, jianwei.zheng@rock-chips.com, yue.long@rock-chips.com References: <1755828118-21640-1-git-send-email-william.wu@rock-chips.com> From: William Wu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-HM-Tid: 0a98df4b4d9709d4kunm3b6efc731b10cc1 X-HM-MType: 1 X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFDSUNOT01LS0k3V1ktWUFJV1kPCRoVCBIfWUFZGh4YGVZJSk5OS0wfSh0ZSENWFRQJFh oXVRMBExYaEhckFA4PWVdZGBILWUFZTkNVSUlVTFVKSk9ZV1kWGg8SFR0UWUFZT0tIVUJCSU5LVU pLS1VKQktCWQY+ DKIM-Signature: a=rsa-sha256; b=jZTcCQqM5yrjKOFSAtYk0EnwukWfQDkymkU92Bs/8bgdkoPL4iFiWgwJQ0RWrLDRT0s05dijmxWi39X56bJypBnDZJPRelZpNaRs6nQiCRqooJycG19YKE9GFZan4yvA4KXRKygdrWj8BKp8qrjw1L2zGaovhMjvOgSZYCkCrg0=; s=default; c=relaxed/relaxed; d=rock-chips.com; v=1; bh=G4TTjMMxsEMVdyTYcmWj7mnrO5XKGcr4tlqnkm4eDc8=; h=date:mime-version:subject:message-id:from; On 8/22/2025 9:56 PM, Alan Stern wrote: > On Fri, Aug 22, 2025 at 10:01:58AM +0800, William Wu wrote: >> If the hid transfer with size divisible to EPs max packet >> size, it needs to set the req->zero to true, then the usb >> controller can transfer a zero length packet at the end >> according to the USB 2.0 spec. >> >> Signed-off-by: William Wu >> --- >> drivers/usb/gadget/function/f_hid.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c >> index 8e1d1e8..8021af3 100644 >> --- a/drivers/usb/gadget/function/f_hid.c >> +++ b/drivers/usb/gadget/function/f_hid.c >> @@ -511,7 +511,7 @@ static ssize_t f_hidg_write(struct file *file, const char __user *buffer, >> } >> >> req->status = 0; >> - req->zero = 0; >> + req->zero = ((count % hidg->in_ep->maxpacket) == 0); > > Here and below, there is no need to check whether count is divisible by > the maxpacket length. The UDC driver does this for you automatically. > (See the kerneldoc for struct usb_request.) Simply set req->zero to 1. > > Alan Stern Good idea，I checked the UDC drivers (drivers/usb/gadget/udc and dwc2/dwc3), they test if zlp is actually needed if req->zero to 1.> >> req->length = count; >> req->complete = f_hidg_req_complete; >> req->context = hidg; >> @@ -967,7 +967,7 @@ static int hidg_setup(struct usb_function *f, >> return -EOPNOTSUPP; >> >> respond: >> - req->zero = 0; >> + req->zero = ((length % cdev->gadget->ep0->maxpacket) == 0); >> req->length = length; >> status = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC); >> if (status < 0) >> -- >> 2.0.0 > > >