From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by archive.lwn.net (Postfix) with ESMTP id 75AD57D04E for ; Fri, 29 May 2020 13:49:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726845AbgE2NtS (ORCPT ); Fri, 29 May 2020 09:49:18 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:39492 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725901AbgE2NtS (ORCPT ); Fri, 29 May 2020 09:49:18 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: koike) with ESMTPSA id D6A6D2A4598 Subject: Re: [PATCH v4 0/5] media: add v4l2_pipeline_stream_{enable,disable} To: Tomasz Figa , Dafna Hirschfeld Cc: Laurent Pinchart , Linux Media Mailing List , Ezequiel Garcia , Hans Verkuil , kernel@collabora.com, Dafna Hirschfeld , Sakari Ailus , "open list:ARM/Rockchip SoC..." , Mauro Carvalho Chehab , Shuah Khan , =?UTF-8?Q?Niklas_S=c3=b6derlund?= References: <20200522075522.6190-1-dafna.hirschfeld@collabora.com> <1c8bd467-5a9c-7285-ec23-d0d864a5f938@collabora.com> <20200526185754.GA25880@pendragon.ideasonboard.com> <50929a55-a071-aa09-eb1a-96776c61c147@collabora.com> From: Helen Koike Message-ID: <7ce3e2cb-60ab-bf0f-6d0a-7bcf0c73d6b8@collabora.com> Date: Fri, 29 May 2020 10:49:04 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Archived-At: List-Archive: List-Post: Hi, On 5/29/20 10:27 AM, Tomasz Figa wrote: > [Fixing Niklas's address.] > > On Fri, May 29, 2020 at 3:26 PM Tomasz Figa wrote: >> >> On Thu, May 28, 2020 at 6:21 PM Dafna Hirschfeld >> wrote: >>> >>> Hi Tomasz, Helen, Laurent >>> >>> On 26.05.20 20:57, Laurent Pinchart wrote: >>>> Hi Tomasz, >>>> >>>> On Tue, May 26, 2020 at 06:11:00PM +0200, Tomasz Figa wrote: >>>>> On Fri, May 22, 2020 at 11:06 AM Helen Koike wrote: >>>>>> On 5/22/20 4:55 AM, Dafna Hirschfeld wrote: >>>>>>> Hi, >>>>>>> This is v4 of the patchset that was sent by Helen Koike. >>>>>>> >>>>>>> Media drivers need to iterate through the pipeline and call .s_stream() >>>>>>> callbacks in the subdevices. >>>>>>> >>>>>>> Instead of repeating code, add helpers for this. >>>>>>> >>>>>>> These helpers will go walk through the pipeline only visiting entities >>>>>>> that participates in the stream, i.e. it follows links from sink to source >>>>>>> (and not the opposite). >>>>>>> For example, in a topology like this https://bit.ly/3b2MxjI >>>>>>> calling v4l2_pipeline_stream_enable() from rkisp1_mainpath won't call >>>>>>> .s_stream(true) for rkisp1_resizer_selfpath. >>>>>>> >>>>>>> stream_count variable was added in v4l2_subdevice to handle nested calls >>>>>>> to the helpers. >>>>>>> This is useful when the driver allows streaming from more then one >>>>>>> capture device sharing subdevices. >>>>>> >>>>>> If I understand correctly, this isn't true anymore right? Nested calls aren't >>>>>> possible anymore since this version doesn't contain stream_count in struct v4l2_subdevice. >>>>>> >>>>>> Documentation of v4l2_pipeline_stream_*() should also be updated. >>>>>> >>>>>> Just to be clear, without the nested call, vimc will require to add its own >>>>>> counters, patch https://patchwork.kernel.org/patch/10948833/ will be >>>>>> required again to allow multi streaming. >>>>>> >>>>>> Also, patch "media: staging: rkisp1: cap: use v4l2_pipeline_stream_{enable,disable}" >>>>>> is cleaner in the previous version (with stream_count in struct v4l2_subdevice). >>>>>> >>>>>> All drivers that allows multi streaming will need to implement some special handling. >>>>>> >>>>>> Adding stream_count in struct v4l2_subdevice still seems cleaner to me. I'd like to hear >>>>>> what others think. >>>>> >>>>> I certainly would see this reference counting done in generic code, >>>>> because requiring every driver to do it simply adds to the endless >>> >>> It is required only for drivers that support multistreaming. I don't know much >>> about other driver except of the ones I am working on, is it a common case? >>> >> >> I'm not very familiar with the older camera I/F drivers, but multiple >> streams isn't anything unusual for camera hardware. I recall the old >> Samsung FIMC already having support for separate preview and capture >> outputs. >> >> Also adding the reference counting on framework level probably >> wouldn't really hurt drivers which only have 1 stream anyway. >> >>>>> amount of boiler plate that V4L2 currently requires from the drivers. >>>>> :( >>>>> >>>>> I wonder if it wouldn't be possible to redesign the framework so that >>>>> .s_stream() at the subdev level is only called when it's expected to >>>>> either start or stop this particular subdev and driver's >>>>> implementation can simply execute the requested action. >>> >>> You mean that a generic code similar to the helper functions in this patchset >>> will be used for all drivers, so that drivers don't call s_stream for subdevices >>> anymore? >>> Anyway, this patchset just adds helper functions, it does not redesign the code. >>> Maybe the stream_count can be updated in the v4l2_subdev_call macro ? >>> This why it can be used not just for the helper functions. >> >> Sorry, just thinking out loud. Generally if we look at other kAPIs, >> such as the drm_crtc_helper_funcs [1] or regulator_ops [2], the driver >> provided implementation doesn't have to care about duplicate >> enable/disable requests. Thanks for this pointer. >> >> [1] https://elixir.bootlin.com/linux/v5.7-rc7/source/include/drm/drm_modeset_helper_vtables.h#L61 >> [2] https://elixir.bootlin.com/linux/v5.7-rc7/source/include/linux/regulator/driver.h#L144 >> >> If we could prohibit calling v4l2_subdev_ops::s_stream() by the >> drivers directly and instead add something like >> v4l2_subdev_s_stream(), the latter could do reference counting on its >> own and then only call v4l2_subdev_ops::s_stream() when the reference >> count changes between 0 and 1. This is basically how v3 was implemented https://patchwork.kernel.org/patch/11489583/ And the main concern (from what I understood) was to add a stream_count under struct v4l2_subdev, that is only touched by the helpers, so this stream_count field would be useless for drivers not using the helpers. which, imho, it is not a big problem. I think we gain more with a common implementation. >> >> One problem I see with this series is that I'm not sure if it's always >> guaranteed that all the drivers in the pipeline would actually use the >> generic helpers. I'm not sure we should always guarantee usage of generic helpers, since drivers may want to initialize subdevices in a specific order. >> If there is a driver in the pipeline which just calls >> v4l2_subdev_ops::s_stream() on some other subdev on its own, it >> wouldn't be aware of the reference count and bad things could happen >> (e.g. the subdev stopped despite the count being > 0). I don't think this is a problem, since v4l2_subdev_ops::s_stream() are usually triggered by a STREAM_ON on a video node. So or the video node driver uses the helpers, or it calls v4l2_subdev_ops::s_stream() on subdevices directly. Unless if, we could have a case where we have multiple video nodes in the same topology that is implemented by different drivers, which seems odd to me. Regards, Helen >> >> However, I'm afraid this is more of the kAPI design issue and could be >> require quite a significant effort to be straightened out. >> >> Best regards, >> Tomasz >> >>> >>> Thanks, >>> Dafna >>> >>>> >>>> I'd very much like that. Note that I think a few drivers abuse the on >>>> parameter to the function to pass other values than 0 or 1. We'd have to >>>> fix those first (or maybe it has been done already, it's been a long >>>> time since I last checked). >>>>