From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88D47C4360D for ; Wed, 25 Sep 2019 16:43:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69FAE21D7A for ; Wed, 25 Sep 2019 16:43:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2439855AbfIYQnI (ORCPT ); Wed, 25 Sep 2019 12:43:08 -0400 Received: from lb3-smtp-cloud9.xs4all.net ([194.109.24.30]:45343 "EHLO lb3-smtp-cloud9.xs4all.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732923AbfIYQnI (ORCPT ); Wed, 25 Sep 2019 12:43:08 -0400 Received: from [192.168.2.10] ([46.9.232.237]) by smtp-cloud9.xs4all.net with ESMTPA id DANaiLbsHz6EADANdiBgjX; Wed, 25 Sep 2019 18:43:06 +0200 Subject: Re: [PATCH] media: vidioc-queryctrl.rst: clarify combining READ_ONLY with WRITE_ONLY To: Helen Koike , mchehab@kernel.org, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, kernel@collabora.com References: <20190925150945.27706-1-helen.koike@collabora.com> <211b3d26-ffbc-3245-6613-7fd42c65cc80@xs4all.nl> From: Hans Verkuil Message-ID: Date: Wed, 25 Sep 2019 18:43:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-CMAE-Envelope: MS4wfERSPoQyAvf5cEaQ19pJx+nQOpyDj770YEWzMb6Rn499daZnpOJjrGH3s8dOHl2ItwJAb/kLHAT81WqgjkM4yqDcTIyWxq1yBCMiInQ4kupACO4El6Iw sK5GRr2Baio8DUxpJqHB80zUsi/x9j17KFqjEaYHhNoRE6yhgfs712g/xYQiYCwaNiyD7KLsktIl7CQMUP2kJMdmz8C6I38YPwONp/7a1hS7g+QwCOAhryF5 M4gjf14NiLj8c6Gu+rIyD9AVQ3ENgp6AjvsPzluV0psnRlzojxnIHPzZuh9KiJUDLhy1fqCUUaH1GZCNu+E6RzXLXn2RuawS4bnk/QqWNDs= Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/25/19 6:29 PM, Helen Koike wrote: > Hi Hans > > On 9/25/19 12:17 PM, Hans Verkuil wrote: >> On 9/25/19 5:09 PM, Helen Koike wrote: >>> Make it clear in the documentation that V4L2_CTRL_FLAG_READ_ONLY doesn't >>> conflict with V4L2_CTRL_FLAG_WRITE_ONLY. Also make it clear that >>> if both are combined then the control has read and write permissions. >> >> That doesn't look right. >> >> This is the test in v4l2-compliance: >> >> __u32 rw_mask = V4L2_CTRL_FLAG_READ_ONLY | V4L2_CTRL_FLAG_WRITE_ONLY; >> >> if ((fl & rw_mask) == rw_mask) >> return fail("can't read nor write this control\n"); >> >> If both flags are set, then a fail is reported. >> >> Did you mis-read? >> >> Setting both flags makes no sense. > > Maybe I misunderstood the V4L2_CTRL_TYPE_CTRL_CLASS, from v4l2-compliance: > > case V4L2_CTRL_TYPE_CTRL_CLASS: > if (fl != (V4L2_CTRL_FLAG_READ_ONLY | V4L2_CTRL_FLAG_WRITE_ONLY)) > return fail("invalid flags for control class\n"); > > I was confused why vivid was using both flags in vivid_ctrl_class (and also the debayer patch that was following this model). > > Why both flags are expected when this type is used? Ah, now I understand. This is specific to control classes: such controls cannot be read nor written. They just provide a name for the control class, but both G_CTRL and S_CTRL should fail. So this specific combination of flags is specific to control classes only. This works because a 'get' will fail if WRITE_ONLY is set, and a 'set' will fail if READ_ONLY is set. Setting both flags will cause both 'get' and 'set' to fail. It is admittedly a bit confusing. Regards, Hans > > Thanks, > Helen > >> >> Regards, >> >> Hans >> >>> >>> Signed-off-by: Helen Koike >>> >>> --- >>> Hi, >>> >>> v4l2-compliance expects both flags for read and write permissions, so I >>> would like to make it clear in the docs. >>> Please let me know if this is not the case. >>> >>> Thanks >>> Helen >>> --- >>> Documentation/media/uapi/v4l/vidioc-queryctrl.rst | 10 ++++++++++ >>> 1 file changed, 10 insertions(+) >>> >>> diff --git a/Documentation/media/uapi/v4l/vidioc-queryctrl.rst b/Documentation/media/uapi/v4l/vidioc-queryctrl.rst >>> index a3d56ffbf4cc..1d3aecdf679f 100644 >>> --- a/Documentation/media/uapi/v4l/vidioc-queryctrl.rst >>> +++ b/Documentation/media/uapi/v4l/vidioc-queryctrl.rst >>> @@ -500,6 +500,11 @@ See also the examples in :ref:`control`. >>> - 0x0004 >>> - This control is permanently readable only. Any attempt to change >>> the control will result in an ``EINVAL`` error code. >>> + >>> + .. note:: >>> + >>> + If combined with ``V4L2_CTRL_FLAG_WRITE_ONLY``, then both, read >>> + and write are allowed. >>> * - ``V4L2_CTRL_FLAG_UPDATE`` >>> - 0x0008 >>> - A hint that changing this control may affect the value of other >>> @@ -523,6 +528,11 @@ See also the examples in :ref:`control`. >>> where writing a value will cause the device to carry out a given >>> action (e. g. motor control) but no meaningful value can be >>> returned. >>> + >>> + .. note:: >>> + >>> + If combined with ``V4L2_CTRL_FLAG_READ_ONLY``, then both, read >>> + and write are allowed. >>> * - ``V4L2_CTRL_FLAG_VOLATILE`` >>> - 0x0080 >>> - This control is volatile, which means that the value of the >>> >>