Re: [PATCH 00/14] staging: vc04_services: bcm2835-isp support

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Stefan,

On Fri, Dec 02, 2022 at 01:41:53PM +0100, Stefan Wahren wrote:
> Am 02.12.22 um 12:23 schrieb Dave Stevenson:
> > 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.
>
> Thanks for clarification. Okay, so Unicam + bcm2835-isp are able to 
> handle the old camera (OV5647)?

Yes, but only for applications using libcamera, directly or indirectly
(through GStreamer for instance, or the V4L2 LD_PRELOAD-ed compatibility
later), not natively through V4L2 only.

> > 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.
> >
> > 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?
> > Dropping anything prior to those points would be rather premature in my book.
> >
> >
> > 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.
> > Actually bcm2835_defconfig appears to only allocate a 32MB CMA heap,
> > so perhaps we don't get very far.
>
> CMA configuration should actually happen in device tree or kernel 
> cmdline. The bcm2835_defconfig is limited to make it work even with the 
> original Pi.
>
> > 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.
> 
> No, it's the vchiq interface which needs the work.
> 
> >>> [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