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

[Stefan Wahren]

Hi Dave,

Am 02.12.22 um 14:42 schrieb Dave Stevenson:
> Hi Stefan
>
> On Fri, 2 Dec 2022 at 12:41, Stefan Wahren <stefan.wahren@xxxxxxxx> wrote:
> > Hi Dave,
> >
> > Am 02.12.22 um 12:23 schrieb Dave Stevenson:
> > > Hi Laurent, Umang, and Stefan.
> > >
> > > On Fri, 2 Dec 2022 at 09:17, Laurent Pinchart
> > > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
> > > > Hi Umang,
> > > >
> > > > 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)?
> There are kernel drivers in mainline for ov5647 (v1) and imx219 (v2)
> cameras, with imx477 (HQ camera) due to be done. Connected to
> bcm2835-unicam that gives you raw images from these sensors.
>
> However you have to use libcamera to get useful images with these
> drivers - raw Bayer isn't easy to consume.
> Libcamera has support for all three (and more) sensors in the RPi IPA
> (image processing algorithms), and will make use of bcm2835-isp to
> process the images appropriately.
>
> > > 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.
> It's the original 256MB Pis that are the issue as memory is so tight.
> Losing a bigger chunk to CMA is a problem there.
>
> I see that bcm283x.dtsi sets it to 64MB, which is probably sufficient
> for most bcm2835-camera use cases, but leaves me worried that you'll
> steal it from other things.
>
> > > 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.
> OK, I'll liaise with Umang and may look to deal with a couple of them.
> Things like documenting the memory barriers probably falls to Phil.

actually this item is already done. I missed to update the TODO file and 
send a patch soon.

Best regards

>    Dave
>
> > Thanks Stefan
> >
> > >     Dave
> > >
> > > > > [1]: https://lore.kernel.org/linux-media/20220208155027.891055-5-jeanmichel.hautbois@xxxxxxxxxxxxxxxx/
> > > > >
> > > > > > > > > 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@xxxxxxxxxx/
> > > > > > > >
> > > > > > > > > > Unfortuntately i hadn't much time to work on vchiq by myself.
> > > > > > > > > >
> > > > > > > > > > Just my two cents
> > > > > > > > > > Stefan
> > > > --
> > > > Regards,
> > > >
> > > > Laurent Pinchart
> > > _______________________________________________
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> > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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