From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2CF5138A726; Fri, 19 Jun 2026 13:06:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781874392; cv=none; b=Y0kMc0G+xZ80VpsUTXF91VM6kNDsphYkfXQKElOO4b98QGA8RrHbdTbUSM8YHg9Gz7GoMbQfFhNtGi5IQJRfpmAB9Pec7VG4yZc/bgoIwqlPW/XMmq7rQ2NqvBtzSlM/CKkEd121p75iahOIeynU6ca6F5LfKwM5UJEEPhVKOo8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781874392; c=relaxed/simple; bh=XRpnFaAYD4JxTpfRYfnNlSejvTVS21ZFpueMCnBrIYc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=POEFvx806BDLEts/yCb6kgQfYIbJLi4aNxNDOOT7Dt670Xu+HsJSiiivyLHijNSo3Z/c402OR/kAWfd5r252hLjbGC+hz78rRVT1jzNLMdt/RazctxxibDhJKMl6qXlZ+T4HeoOLllr9ljL2foRW7bN7XGr7G1AYypXiu/ryisU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c8lS+RKp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="c8lS+RKp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 86E2F1F000E9; Fri, 19 Jun 2026 13:06:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781874388; bh=B0QjJ0r3T1RYk1i9XytkOvWkCThvCLDC0VRduOm6DpQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=c8lS+RKpnAd1keGtLeakexrPve2/AQukDtnReKQWodsuTXoqc3RmD3YqH6q0lM1zn NVAaXx10iVv8pWPUkPoTxE4SH4JOvXxa8uwp5XMP4fOVkaXNfTZSM2bpG6/D4i0WTA heDp4lq5naMqkEao5PRUbl9xn9RHjZfgCj8uEMmUbOC44Djo7Q+IMfWi2jWfMFRMll kN7/Ur3tv+Slwilh/PhJeiQ+xebFleAod0+7JHdnWxDdxR1/QUVt3mx1WEXUO3D4iq BAUwTQmaOeVPvaTV2lXGR8JyLy7GiyX16HT2imNFvxb9qtjav04G/GCHaUpuJewbS2 OG+jWtzJDxOOQ== Received: from mchehab by mail.kernel.org with local (Exim 4.99.4) (envelope-from ) id 1waYvS-00000000uOT-18em; Fri, 19 Jun 2026 15:06:26 +0200 Date: Fri, 19 Jun 2026 15:06:26 +0200 From: Mauro Carvalho Chehab To: Detlev Casanova Cc: Mauro Carvalho Chehab , Nicolas Dufresne , Benjamin Gaignard , Philipp Zabel , Ezequiel Garcia , Heiko Stuebner , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rockchip@lists.infradead.org, kernel@collabora.com, linux-arm-kernel@lists.infradead.org, Christopher Healy Subject: Re: [PATCH v2 2/5] docs: media: add documentation for media client usage stats Message-ID: References: <20260617-v4l2-add-fdinfo-v2-0-d298e98ce06a@collabora.com> <20260617-v4l2-add-fdinfo-v2-2-d298e98ce06a@collabora.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: <20260617-v4l2-add-fdinfo-v2-2-d298e98ce06a@collabora.com> Sender: Mauro Carvalho Chehab On Wed, Jun 17, 2026 at 02:10:57PM -0400, Detlev Casanova wrote: > From: Christopher Healy > > Document the media fdinfo interface for per-file-descriptor usage > statistics exposed by stateless V4L2 codec drivers via > /proc//fdinfo/. > > This interface is designed for stateless (request API based) codec > devices where the kernel driver has per-job visibility into hardware > execution. Stateful codecs cannot support all of this because their > firmware manages job scheduling opaquely. > > The specification defines media- prefixed keys for engine utilization > time, and operating frequency, following the same conventions as the DRM > fdinfo mechanism documented in drm-usage-stats.rst. > > More fields can be added later. > > Signed-off-by: Christopher Healy > Signed-off-by: Detlev Casanova > --- > .../userspace-api/media/drivers/index.rst | 1 + > .../media/drivers/media-usage-stats.rst | 85 ++++++++++++++++++++++ Please notice that sysfs/procfs APIs are usually documented at Documentation/ABI/, using a machine-readable format[1]. Still, we do want it also at media uAPI. So, please add it there as well on your next spin. [1] As those are new, Documentation/ABI/testing/ is probably the best place. > 2 files changed, 86 insertions(+) > > diff --git a/Documentation/userspace-api/media/drivers/index.rst b/Documentation/userspace-api/media/drivers/index.rst > index 02967c9b18d6..61879738836c 100644 > --- a/Documentation/userspace-api/media/drivers/index.rst > +++ b/Documentation/userspace-api/media/drivers/index.rst > @@ -34,6 +34,7 @@ For more details see the file COPYING in the source distribution of Linux. > imx-uapi > mali-c55 > max2175 > + media-usage-stats > npcm-video > omap3isp-uapi > thp7312 > diff --git a/Documentation/userspace-api/media/drivers/media-usage-stats.rst b/Documentation/userspace-api/media/drivers/media-usage-stats.rst > new file mode 100644 > index 000000000000..d3dc07002f62 > --- /dev/null > +++ b/Documentation/userspace-api/media/drivers/media-usage-stats.rst > @@ -0,0 +1,85 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +.. _media-usage-stats: > + > +========================== > +Media client usage stats > +========================== > + > +Stateless V4L2 codec drivers can optionally expose per-file-descriptor usage > +statistics via ``/proc//fdinfo/``. This is analogous to the DRM fdinfo > +mechanism documented in :ref:`drm-client-usage-stats`, but uses the ``media-`` > +key prefix for V4L2 media devices. > + > +This interface is specific to stateless (request API based) codec devices, > +including both decoders and encoders. With stateless codecs, the kernel driver > +explicitly submits each frame to the hardware and receives a completion > +interrupt, providing a clean per-job boundary that can be attributed to the > +submitting file descriptor. > + > +Stateful codec devices cannot support this interface because their firmware > +manages job scheduling internally. The kernel driver submits bitstream data > +but has no visibility into per-frame hardware execution timing. > + > +Implementation > +============== > + > +The V4L2 core provides the plumbing: drivers implement the ``show_fdinfo`` > +callback in ``struct v4l2_file_operations``, and the core wires it into the > +kernel ``struct file_operations`` so that ``/proc//fdinfo/`` output > +includes the driver-provided keys. > + > +File format specification > +========================= > + > +- File shall contain one key value pair per one line of text. > +- Colon character (``:``) must be used to delimit keys and values. > +- All standardised keys shall be prefixed with ``media-``. > +- Driver-specific keys shall be prefixed with ``driver_name-``. > + > +Mandatory keys > +-------------- > + > +- media-driver: > + > + String shall contain the name of the media driver. > + > +- media-type: > + > + String shall identify the type of media engine exposed through this file > + descriptor. Standard values are ``decoder`` and ``encoder``. > + > +Utilization keys > +---------------- > + > +- media-engine-usage: ns > + > + Time in nanoseconds that the hardware engine spent busy processing work > + belonging to this file descriptor. The engine being measured is identified > + by the ``media-type`` key. > + > + Values are not required to be constantly monotonic if it makes the driver > + implementation easier, but are required to catch up with the previously > + reported larger value within a reasonable period. > + > +Frequency keys > +-------------- > + > +- media-maxfreq: Hz > + > + Maximum operating frequency of the main engine clock. > + > +- media-curfreq: Hz > + > + Current operating frequency of the main engine clock. > + > +Example output > +============== > + > +:: > + > + media-driver: hantro-vpu > + media-type: decoder > + media-engine-usage: 123456789 ns > + media-maxfreq: 600000000 Hz > + media-curfreq: 600000000 Hz > > -- > 2.54.0 > -- Thanks, Mauro