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Date:   Fri, 2 Dec 2022 15:29:00 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Dave Stevenson <dave.stevenson@raspberrypi.com>
Cc:     Umang Jain <umang.jain@ideasonboard.com>,
        Stefan Wahren <stefan.wahren@i2se.com>,
        linux-media@vger.kernel.org, kernel-list@raspberrypi.com,
        linux-kernel@vger.kernel.org, linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org,
        linux-staging@lists.linux.dev,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@broadcom.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Naushir Patuck <naush@raspberrypi.com>,
        David Plowman <david.plowman@raspberrypi.com>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>
Subject: Re: [PATCH 00/14] staging: vc04_services: bcm2835-isp support
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Hi Dave,

On Fri, Dec 02, 2022 at 12:38:09PM +0000, Dave Stevenson wrote:
> On Fri, 2 Dec 2022 at 12:10, Laurent Pinchart wrote:
> > On Fri, Dec 02, 2022 at 11:23:29AM +0000, Dave Stevenson wrote:
> > > On Fri, 2 Dec 2022 at 09:17, Laurent Pinchart wrote:
> > > > On Fri, Dec 02, 2022 at 11:57:18AM +0800, Umang Jain wrote:
> > > > > On 12/2/22 6:45 AM, Stefan Wahren wrote:
> > > > > > Am 30.11.22 um 11:58 schrieb Umang Jain:
> > > > > >> On 11/27/22 6:56 AM, Stefan Wahren wrote:
> > > > > >>> Am 26.11.22 um 17:26 schrieb Umang Jain:
> > > > > >>>> On 11/26/22 8:12 PM, Stefan Wahren wrote:
> > > > > >>>>> Am 21.11.22 um 22:47 schrieb Umang Jain:
> > > > > >>>>>> This series aims to upport bcm2835-isp from the RPi kernel [1] and is a
> > > > > >>>>>> independent subset of earlier series [2] posted to upport CSI-2/CCP2
> > > > > >>>>>> receiver IP core("Unicam) + the ISP driver found in BCM283x and compatible
> > > > > >>>>>> SoCs (namely BCM2711). Unicam is still under active development to work
> > > > > >>>>>> with multistream support to get into mainline. Hence only the ISP driver
> > > > > >>>>>> will remain the primary area of this series.
> > > > > >>>>>
> > > > > >>>>> thanks for working on this. But honestly i would prefer that vchiq
> > > > > >>>>> comes out of staging before adding more features. As Greg said
> > > > > >>>>> some time ago staging is not a place to "dump code and run away".
> > > > > >>>>> These new files are in the same bad shape as the rest of vc04
> > > > > >>>>> before the clean-up here in staging started.
> > > > > >>>>
> > > > > >>>> Certainly, I am not here to do that - but I am still learning the ropes.
> > > > > >>>
> > > > > >>> no problem.
> > > > > >>>
> > > > > >>>> If the staging issue is becoming a blocker for bcm2835-isp going
> > > > > >>>> upstream, I would be happy to help here! Though I must mention that
> > > > > >>>> I still have limited visibility so my aim would be to chart out a
> > > > > >>>> plan of things needed to be done to get vc04_services out of staging!
> > > > > >>>
> > > > > >>> The vchiq driver is in staging since 2016, so every step forwards is
> > > > > >>> good. Unfortunately all of the low hanging fruits has been gathered.
> > > > > >>>
> > > > > >>> For me the most important, but not to tricky steps to get vchiq out
> > > > > >>> of staging would be:
> > > > > >>>
> > > > > >>> * Cleanup logging mechanism
> > > > > >>>
> > > > > >>> * Get rid of custom function return values
> > > > > >>>
> > > > > >>> There was already an attempt for this [1]
> > > > > >>>
> > > > > >>> * Get rid of all non essential global structures and create a proper per
> > > > > >>> device structure
> > > > > >>>
> > > > > >>>>> I agree that VCSM is on the TODO list for vchiq, but this driver
> > > > > >>>>> is not necessary for making bcm2835-audio & bcm2835-camera leave
> > > > > >>>>> staging. It just binds more resources on a new feature.
> > > > > >>
> > > > > >> bcm2835-camera is the legacy camera stack which probably need to be
> > > > > >> dropped from hereon...
> > > > > >
> > > > > > I don't not know if there any users left, so i would be careful here.
> > > > > > Can bcm2835-isp completely replace bcm2835-camera? Sorry, for this
> > > > > > dumb question but i'm not expert here.
> > > > >
> > > > > I am careful too here and probably need Input from RaspberryPi in order
> > > > > to proceed to drop it. But from my perspective - bcm2835-camera is _not_
> > > > > going out of staging - it'll either sit here (or probably dropped) as
> > > > > statied from [1]
> > > > >
> > > > > ```
> > > > > + * There are two camera drivers in the kernel for BCM283x - this one
> > > > > + * and bcm2835-camera (currently in staging).
> > > > > ```
> > > > >
> > > > > The bcm2835-camera is meant to be replaced by unicam [1] , but the ISP
> > > > > (bcm2835-isp) is meant to be worked with unicam [1]. In fact, I have
> > > > > mentioned in my cover the testing of bcm2835-isp happened on top of
> > > > > unicam patches.
> > > >
> > > > To be accurate, the bcm2835-camera driver supports the VC4
> > > > firmware-based camera stack. In that setup, the camera sensors (OV5647
> > > > or IMX219), CSI-2 receiver (Unicam) and ISP are all controlled by the
> > > > firmware, which provides a high-level interface towards the kernel. This
> > > > architecture has been replaced by Linux-side control of the camera
> > > > sensors (through existing drivers in drivers/media/i2c/), Unicam
> > > > (through the driver from [1]) and ISP (through this driver). Moving
> > > > control to the Linux side requires complex processing in userspace,
> > > > handled by libcamera.
> > > >
> > > > bcm2835-camera is thus replaced by multiple drivers combined with
> > > > libcamera, and that is the camera stack that is shipped by Raspberry Pi
> > > > these days. While this may affect some userspace use cases), we will not
> > > > work on destaging bcm2835-camera, and as far as I'm aware, nobody else
> > > > is planning to do so either. I don't mind much if the driver stays in
> > > > staging for some more time, but I'd rather drop it if possible.
> > >
> > > It would be reasonable to drop it at the point that Libcamera can work
> > > to a similar level with at least the following list of applications:
> > > - FFmpeg
> > > - Gstreamer
> > > - Chromium
> > > - Firefox
> > > - Motion
> > > And that still leaves a huge number of existing V4L2 apps out in the cold.
> >
> > That's exactly the kind of input we were looking for, thanks.
> 
> Please note that those are only the 5 major ones that came immediately
> to mind as having significant numbers of users. There are obviously
> many more V4L2 apps around which currently "just work" if they use the
> API correctly.

Sure, I'll keep that in mind.

> > GStreamer is already addressed.
> >
> > Chromium and Firefox will go through PipeWire. There is a working
> > implementation in libwebrtc, Kieran may be able to comment on the
> > upstreaming state. It will take some time for distributions to switch,
> > and I can't predict the time line, but that seems to clearly be the
> > direction the Linux desktop is taking.
> >
> > I haven't looked at FFmpeg yet (maybe someone has ?). It probably makes
> > sense to add native libcamera support to FFmpeg, even if PipeWire
> > support could also make sense. It could also make sense to expose in the
> > libcamera V4L2 compat layer the libv4l2 API functions, as that would
> > allow linking FFmpeg (when compiled with CONFIG_LIBV4L2) to libcamera
> > instead of libv4l2, but Debian doesn't set CONFIG_LIBV4L2, so this isn't
> > an immediate solution to the problem.
> 
> Native would be nice in my book, but isn't always as straightforward.

I agree, native would be good.

> > Same thing for motion, except it has no libv4l2 support. The V4L2 compat
> > layer could still be used with LD_PRELOAD, but that's not a great
> > solution. Native libcamera support would make more sense (or possibly
> > even GStreamer support, I don't know if upstream would accept that).
> 
> The main bit missing with the compat layer is controls. AIUI fixing
> that isn't a priority.

Good point. That's something we should fix. Not a high priority indeed,
but still good to have (and it shouldn't take too long).

> Things like Motion being used for security purposes need to be able to
> set properties like exposure modes in order to achieve usable images
> under changing lighting conditions.
> 
> > In a side note, how do the above applications work today on Raspberry Pi
> > platforms that use a sensor not supported by the legacy camera stack ?
> 
> They don't for raw sensors, but do work with USB webcams.
> Raspberry Pi have sold camera modules since 2013 (OV5647), with v2
> (IMX219) coming along in 2016, and HQ (IMX477) in 2020. Linux has only
> had frameworks to sensibly support raw image sensors since libcamera
> came on the scene around 2019.

Do I understand correctly that the need to keep bcm2835-camera working
is for support of the v1 and v2 camera modules only ? Or are there other
use cases ?

> > > Do you wish to make any predictions as to when that would be
> > > achievable? Or even when a v1.0 release of libcamera is going to
> > > happen?
> >
> > Now that we have started tagging releases, we've also decided to publish
> > a roadmap with the development still needed to stabilize the API. We'll
> > likely start working on it this month.
> >
> > > Dropping anything prior to those points would be rather premature in my book.
> >
> > Something I forgot to mention is that there should be no issue at all
> > keeping bcm2835-camera fully supported in the Raspberry Pi downstream
> > kernel for a longer period of time. It's in upstream that I don't think
> > it should be destaged, as it's already considered legacy and should be
> > phased out. Do you know if there are users of that driver with a
> > mainline kernel ?
> 
> There are a number of distros that use mainline kernels rather than
> our vendor kernel. I don't follow distros in detail, but I believe
> both Gentoo and Opensuse fall into that category.
>  Any users of the camera module under those will be using the mainline
> bcm2835-camera module. I have no stats for who uses those on a Pi.

OK.

> > > The TODOs on bcm2835-camera are:
> > > 1) Zero copy. That comes almost for free as bcm2835-isp already does
> > > this, but it does rely on vcsm-cma.
> > > The main reason I haven't pushed it is that it then requires
> > > reasonable amounts of CMA heap for all the buffers, which until
> > > recently haven't been present in the default configurations. With the
> > > vc4 DRM driver now being default (at least for the vendor kernel) and
> > > also requiring CMA, making the change makes more sense.
> > > AFAIK there is no easy way to have one driver choosing between using
> > > vb2_vmalloc_memops and vb2_dma_contig_memops at runtime, but I may be
> > > wrong.
> >
> > Some drivers use a module parameter for that, but that's not great.
> 
> I had thought of a module parameter, but it becomes yet another
> configuration thing to get incorrectly set.
> Perhaps Kconfig based on the setting for CMA_SIZE_MBYTES, but that can
> be overridden.

The trouble with vb2-vmalloc is that you'll end up copying data, which I
expect to cause various performance issues that may generate bug reports
difficult to address. Increasing the CMA size would be better.

> > > Actually bcm2835_defconfig appears to only allocate a 32MB CMA heap,
> > > so perhaps we don't get very far.
> > >
> > > 2) This isn't workable within the current V4L2 frameworks. The
> > > multi-planar V4L2 pixel formats are currently allocated as independent
> > > buffers for each plane, whereas the firmware needs a single buffer
> > > with (currently) specific offsets for the chroma planes. The
> > > V4L2/videobuf2 core changes required to implement that are going to be
> > > significant, and have minimal gain.
> > > The specific stride handling is already dealt with (set bytesperline
> > > appropriately), it's the padding of the height to a multiple of 16
> > > before the chroma planes on YUV420 and NV12 formats that require the
> > > firmware to do a small amount of repacking. The performance hit is
> > > actually minimal anyway.
> > >
> > > If bcm2835-camera is the only thing holding back vc04_services, then I
> > > can have a look at it.
> >
> > I'll let Umang comment on whether it's holding vc04_services back, but
> > my understanding it that we could destage vc04_services while keeping
> > bcm2835-camera in staging for the time being. If anyone disagrees with
> > that, please let me know.
> >
> > > > > [1]: https://lore.kernel.org/linux-media/20220208155027.891055-5-jeanmichel.hautbois@ideasonboard.com/
> > > > >
> > > > > >>>>
> > > > > >>>> I see two TODO files in vc04_services:
> > > > > >>>>     ./bcm2835-camera/TODO
> > > > > >>>>     ./interface/TODO
> > > > > >>>>
> > > > > >>>> One of the bcm2835-camera TODO points to the vc-sm-cma driver
> > > > > >>>> itself. So that's address in the series. The other remaining one -
> > > > > >>>> I will need to take a deeper look before commenting on it.
> > > > > >>>>
> > > > > >>>> The main chunk of TODO are in vc04_services/interfaces/TODO. Doing
> > > > > >>>> a cursory reading of them suggests that these apply to *all*
> > > > > >>>> vc04_services components? Am I right?
> > > > > >>>
> > > > > >>> Actually these applies just for the interfaces directory. Some of
> > > > > >>> them could apply to the services, but this is no priority.
> > > > > >>
> > > > > >> By no priority, you mean this doesn't affect the criteria required to
> > > > > >> ful-fill to get these out of staging?
> > > > > >
> > > > > > Correct
> > > > > >
> > > > > >>>> Are these are the specific bits of cleanup you are referring to in
> > > > > >>>> your comment?
> > > > > >>>
> > > > > >>> You mean about bcm2835-isp? There were too many changes to vchiq
> > > > > >>> that i don't remember them all. The first that come to my mind was
> > > > > >>> those fancy comment sections which is not kernel coding style. It
> > > > > >>> has been removed.
> > > > > >>
> > > > > >> No, I don't mean the bcm2835-isp changes (those are upcoming /
> > > > > >> out-of-tree still so...). I mean what are the specific bits / points
> > > > > >> that needs to be addressed to get vc04_services out of the staging.
> > > > > >
> > > > > > These were the points which i mentioned in my last email. They came
> > > > > > from interface/TODO.
> > > > > >
> > > > > >> You have mentioned it above now, so I'll follow up on those.
> > > > > >
> > > > > > That would be great :)
> > > > > >
> > > > > >> The many vchiq changes you referred to above comment (that you don't
> > > > > >> remember) are from [1] as well or some other series ?
> > > > > >
> > > > > > Sorry, for the confusing. The many changes i refer were the dozens of
> > > > > > clean up patches for vc04_interfaces in mainline staging since the
> > > > > > last years. [1] was just a single patch which has been accepted yet.
> > > > >
> > > > > Ah I see. There are many others that I've to dig out then. Thanks for
> > > > > clarifying!
> > > > >
> > > > > >>> [1] -
> > > > > >>> https://lore.kernel.org/linux-staging/20220712181928.17547-1-jslebodn@redhat.com/
> > > > > >>>
> > > > > >>>>> Unfortuntately i hadn't much time to work on vchiq by myself.
> > > > > >>>>>
> > > > > >>>>> Just my two cents
> > > > > >>>>> Stefan

-- 
Regards,

Laurent Pinchart