From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 2037D1C6B5; Thu, 22 Aug 2024 09:26:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724318802; cv=none; b=A92QnaK/MONgSVtkcplD2kcI86MqHbmxXEM6wPSU4pcQfIlNEo8UmMzstIvgRZ8CZ36u12+wkrdqzpj/HkJNB+Xw1d6TgHoM1qzKYmu488ddcrHwYYRUvO0LQsVEOr+RVYBzv/ePqSZHfCX+cnwgsF3xkPBO7ItFNoHvW3ISwss= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724318802; c=relaxed/simple; bh=FWF9DF1CxrugxkwgdC2uYLB0I3wE7fR9AdLYrKWreIg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WM7p/GyHHP/sLsG/Uu5a9nzFbrVZfG9y4gLauX0bDv8XEHuXeY5SECpDcWIp4eOu/QnaKCfa8Qa0tk0KVTZ+aDH/rHzV8qypvz4p9vELgFhnb9IIvOTPbXXVnRy42GChCOlZS8kzcLjtAAPi5/Mo1UV0TL18/GVTlupWhRg2p5Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dqXViVL3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dqXViVL3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50154C32782; Thu, 22 Aug 2024 09:26:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1724318800; bh=FWF9DF1CxrugxkwgdC2uYLB0I3wE7fR9AdLYrKWreIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dqXViVL3Y0Fpkg03DRV7nAUX7wK7QwcRspkl1+W5U0UQKxMWsRvKJ0Ed6zpBxzFDO HoY1Sh4Hia7X7m97wBgkr6NCzUA3bWBpUQ/mH7pSt0MpR6PxKpXNnIcjkGbzVX1WPZ oLniUOzk9Q0WeSt+bRiyceU935xNE+nNxQPFvmds= Date: Thu, 22 Aug 2024 17:26:38 +0800 From: Greg Kroah-Hartman To: crwulff@gmail.com Cc: linux-usb@vger.kernel.org, Konstantin Aladyshev , David Sands , Jeff Johnson , Christophe JAILLET , linux-kernel@vger.kernel.org, Chris Wulff Subject: Re: [PATCH v5] USB: gadget: f_hid: Add GET_REPORT via userspace IOCTL Message-ID: <2024082225-squad-twerp-ad11@gregkh> References: <20240817142850.1311460-2-crwulff@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240817142850.1311460-2-crwulff@gmail.com> On Sat, Aug 17, 2024 at 10:28:51AM -0400, crwulff@gmail.com wrote: > From: Chris Wulff > > While supporting GET_REPORT is a mandatory request per the HID > specification the current implementation of the GET_REPORT request responds > to the USB Host with an empty reply of the request length. However, some > USB Hosts will request the contents of feature reports via the GET_REPORT > request. In addition, some proprietary HID 'protocols' will expect > different data, for the same report ID, to be to become available in the > feature report by sending a preceding SET_REPORT to the USB Device that > defines what data is to be presented when that feature report is > subsequently retrieved via GET_REPORT (with a very fast < 5ms turn around > between the SET_REPORT and the GET_REPORT). > > There are two other patch sets already submitted for adding GET_REPORT > support. The first [1] allows for pre-priming a list of reports via IOCTLs > which then allows the USB Host to perform the request, with no further > userspace interaction possible during the GET_REPORT request. And another > [2] which allows for a single report to be setup by userspace via IOCTL, > which will be fetched and returned by the kernel for subsequent GET_REPORT > requests by the USB Host, also with no further userspace interaction > possible. > > This patch, while loosely based on both the patch sets, differs by allowing > the option for userspace to respond to each GET_REPORT request by setting > up a poll to notify userspace that a new GET_REPORT request has arrived. To > support this, two extra IOCTLs are supplied. The first of which is used to > retrieve the report ID of the GET_REPORT request (in the case of having > non-zero report IDs in the HID descriptor). The second IOCTL allows for > storing report responses in a list for responding to requests. > > The report responses are stored in a list (it will be either added if it > does not exist or updated if it exists already). A flag (userspace_req) can > be set to whether subsequent requests notify userspace or not. > > Basic operation when a GET_REPORT request arrives from USB Host: > > - If the report ID exists in the list and it is set for immediate return > (i.e. userspace_req == false) then response is sent immediately, > userspace is not notified > > - The report ID does not exist, or exists but is set to notify userspace > (i.e. userspace_req == true) then notify userspace via poll: > > - If userspace responds, and either adds or update the response in > the list and respond to the host with the contents > > - If userspace does not respond within the fixed timeout (2500ms) > but the report has been set prevously, then send 'old' report > contents > > - If userspace does not respond within the fixed timeout (2500ms) > and the report does not exist in the list then send an empty > report > > Note that userspace could 'prime' the report list at any other time. > > While this patch allows for flexibility in how the system responds to > requests, and therefore the HID 'protocols' that could be supported, a > drawback is the time it takes to service the requests and therefore the > maximum throughput that would be achievable. The USB HID Specification > v1.11 itself states that GET_REPORT is not intended for periodic data > polling, so this limitation is not severe. > > Testing on an iMX8M Nano Ultra Lite with a heavy multi-core CPU loading > showed that userspace can typically respond to the GET_REPORT request > within 1200ms - which is well within the 5000ms most operating systems seem > to allow, and within the 2500ms set by this patch. > > [1] https://lore.kernel.org/all/20220805070507.123151-2-sunil@amarulasolutions.com/ > [2] https://lore.kernel.org/all/20220726005824.2817646-1-vi@endrift.com/ > > Signed-off-by: David Sands > Signed-off-by: Chris Wulff > --- > v5: release spinlock on copy_from_user error path > v4: cleaned up a warning > https://lore.kernel.org/all/20240814125525.3917130-2-crwulff@gmail.com/ > v3: rebased to usb-next, checkpatch cleanup (formatting, lore.kernel.org links) > https://lore.kernel.org/all/20240810141834.640887-2-crwulff@gmail.com/ > v2: https://lore.kernel.org/all/CO1PR17MB541952864266039BAA7BBBD3E10F2@CO1PR17MB5419.namprd17.prod.outlook.com/ > v1: https://lore.kernel.org/all/20230215231529.2513236-1-david.sands@biamp.com/ Nice, thanks for sticking with this! greg k-h