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Date:   Thu, 23 Jun 2022 11:19:03 +0200
From:   Jacopo Mondi <jacopo@jmondi.org>
To:     Eugen.Hristev@microchip.com
Cc:     hverkuil@xs4all.nl, linux-arm-kernel@lists.infradead.org,
        linux-media@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Claudiu.Beznea@microchip.com,
        Nicolas.Ferre@microchip.com
Subject: Re: [PATCH v10 0/5] media: atmel: atmel-isc: implement media
 controller
Message-ID: <20220623091903.zedzu5dv3x557lsp@uno.localdomain>
References: <20220503095127.48710-1-eugen.hristev@microchip.com>
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Hi Eugen,

On Thu, Jun 23, 2022 at 08:39:48AM +0000, Eugen.Hristev@microchip.com wrote:
> On 6/22/22 6:46 PM, Jacopo Mondi wrote:
> > Hi Hans,
> >
> > On Wed, Jun 22, 2022 at 04:55:27PM +0200, Hans Verkuil wrote:
> >> Hi Eugen, Jacopo,
> >>
> >> On 22/06/2022 16:14, Jacopo Mondi wrote:
> >>> Hi Hans, Eugen
> >>>
> >>> On Wed, Jun 22, 2022 at 03:47:33PM +0200, Hans Verkuil wrote:
> >>>> On 22/06/2022 14:42, Eugen.Hristev@microchip.com wrote:
> >>>>> On 6/22/22 3:25 PM, Eugen Hristev - M18282 wrote:
> >>>>>> On 6/22/22 2:53 PM, Hans Verkuil wrote:
> >>>>>>> Hi Eugen,
> >>>>>>>
> >>>>>>> On 03/05/2022 11:51, Eugen Hristev wrote:
> >>>>>>>> This series is a split from the series :
> >>>>>>>> [PATCH v9 00/13] media: atmel: atmel-isc: implement media controller
> >>>>>>>> and it includes the media controller part.
> >>>>>>>> previous fixes were sent on a different patch series.
> >>>>>>>>
> >>>>>>>> As discussed on the ML, moving forward with having the media link validate at
> >>>>>>>> start/stop streaming call.
> >>>>>>>> I will test the patch :
> >>>>>>>> [RFC PATCHv2] vb2: add support for (un)prepare_streaming queue ops
> >>>>>>>> afterwards, but that patch requires moving my logic to the new vb2 callbacks.
> >>>>>>>
> >>>>>>> I'm looking at merging this series, but I would like to have the output of
> >>>>>>> 'v4l2-compliance -m /dev/mediaX' to verify that the MC links etc. is all
> >>>>>>> correct.
> >>>>>>
> >>>>>> Hello Hans,
> >>>>>>
> >>>>>> Please have a look at attached file . Unless you want me to add the
> >>>>>> whole output to the e-mail ?
> >>>>>>
> >>>>>> I also added output of media-ctl -p for your convenience.
> >>>>>> the subdev2 is a device and driver that is not upstream and has some
> >>>>>> compliance issues, they are reported by the v4l2-compliance tool, but
> >>>>>> they should not affect this series, it's a synopsys driver that was
> >>>>>> rejected on mainline a few years ago, I took it for internal usage, but
> >>>>>> it's not cleaned up nor worked a lot upon.
> >>>>>>
> >>>>>>>
> >>>>>>> And one more question which may have been answered already in the past:
> >>>>>>>
> >>>>>>> Changing to the MC will break existing applications, doesn't it? Or did I
> >>>>>>> miss something?
> >>>>>>>
> >>>>>>
> >>>>>> The existing applications will have to configure the pipeline now. It
> >>>>>> will no longer work by configuring just the top video node /dev/video0 .
> >>>>>> They would have to use media-ctl for it, something similar with this set
> >>>>>> of commands:
> >>>>>
> >>>>> To add on top of that, actually, the reality is that without the MC
> >>>>> support in atmel-isc , some of our platforms do not work at all, because
> >>>>> the csi2dc driver which is in the middle of the pipeline, is a MC
> >>>>> driver. So it will not work without configuring it with MC anyway. It
> >>>>> used to work in a very preliminary version of the csi2dc driver which I
> >>>>> sent a few years ago, but that way of handling things was rejected.
> >>>>> Hence I changed the csi2dc to being full-MC driver (requested for new
> >>>>> drivers) and now I am completing the conversion for the whole pipeline.
> >>>>> We are using this MC-centric approach in production for our products to
> >>>>> be as close as possible to mainline, and backported it to our 5.15
> >>>>> internal releases, which people are using right now.
> >>>>
> >>>> I'm not all that keen on breaking userspace for those who do NOT use the
> >>>> Atmel BSP. Basically some platforms are currently broken, and with this patch
> >>>> series some other platforms are broken, but at least can be fixed by changing
> >>>> userspace.
> >>>>
> >>>> How feasible is it to do something similar that TI did for the cal driver?
> >>>> (drivers/media/platform/ti/cal)
> >>>>
> >>>> I.e., based on a module option the MC is enabled or disabled. And if a
> >>>> csi2dc is present, then the MC API is always enabled.
> >>>>
> >>>
> >>> I think I have suggested Eugen to move to MC when he
> >>> started looking in libcamera, so sorry for the intrusion but I feel
> >>> a bit bad for not rising the point earlier and get him to v10
> >>>
> >>> I understand your point Hans, and when a vendor upstreaming code or a
> >>> user requires to maintain compatibility, the burden of keeping more
> >>> code in to handle the MC and non-MC cases is worth the complications.
> >>
> >> Eugen, can you provide a list of platforms that will break with this
> >> change and which platforms are currently broken without this series?
>
> Hi Hans,
>
> Basically the sama5d2 platform (we have several versions of the chip :
> sama5d21, sama5d27, sama5d29, in various packages, SIP, SoMs, on many
> different boards ) would be broken. this is the old platform.
> It would be broken if the sensor default format is a mismatch with the
> default format of the ISC .  Basically the old code currently is
> propagating all the frame information down to the sensor, thing that no
> longer happens with this patch series.
>
> The platform that needs MC is mainly sama7g5 , which has a longer
> pipeline, supports CSI2 bus, and has more drivers (the csi2dc is one of
> them ), some are not mainlined.
> Future platforms , which are currently in prototyping, have a similar
> pipeline with sama7g5, some have more complicated pipelines, but they
> include the ISC and we plan to use the same driver.
>
> >>
> >> I'm trying to get a bit of a feel of the potential problems this change
> >> will introduce.
> >>
> >>>
> >>> But if even the vendor wants to move to MC to allow more use-cases I
> >>> think we have to acknolege that if you're running mainline on an
> >>> embedded system you could expect to adjust your setup between kernel
> >>> updates. The idea to document the media-ctl commands required to setup
> >>> the pipeline it's helpful, and might help in the interim period until
> >>> the platform is not supported by libcamera.
> >>
> >> Well, I don't want Linus to start yelling at me for breaking userspace :-)
> >>
> >> We have broken userspace API (intentionally) in the past, but only with
> >> good reasons. And sometimes a driver is used so rarely that it is not worth
> >> the effort to try and keep compatible.
> >>
> >> As a developer I'd love to just forget about the old API, but as subsystem
> >> maintainer I need good arguments.
> >
> > I understand and I think these are all valid concerns. Finding a
> > balance between new features and legacy is not easy.
> >
> >>
> >> Another option might be to take the TI cal approach, but have warnings that
> >> it will be removed in, say, 2 years time. Or even make a copy of the driver
> >> for the old platforms, and perhaps move that to staging to be removed eventually.
> >>
> >> The idea of a sudden breakage when going from kernel K to K+1 doesn't sit
> >> well with me, if there was a transition period of 1-2 years then that would be
> >> better.
> >>
> >
> > If staging works for you that's probably the easiest option. Let's see
> > what Eugen prefers!
>
> Hi Jacopo,
>
> How does the staging solution work ? I do not fully understand the
> options here to make an educated choice

Hans should probably tell, but my interepetation would be to move the
existing driver (before this series) to drivers/staging/ and advance
the existing one in drivers/media/ to MC support.

Users of the old driver interface could keep using the one in (de)staging
for a little longer.

Would changing the driver KConfig symbol name help making the change
more evident maybe ? Users that upgrade to a new kernel will be
notified about the new symbol instead of being silently moved to the new
interface.

Thanks
  j

>
> Thanks for helping out,
>
> Eugen
>
>
> >
> >> Regards,
> >>
> >>        Hans
> >>
> >>>
> >>> That said, if Eugen wants to give the flag a try I won't
> >>> oppose :)
> >>>
> >>>
> >>>> Regards,
> >>>>
> >>>>     Hans
> >>>>
> >>>>>
> >>>>>>
> >>>>>> media-ctl -d /dev/media0 --set-v4l2 '"imx219
> >>>>>> 1-0010":0[fmt:SRGGB10_1X10/1920x1080]'
> >>>>>> media-ctl -d /dev/media0 --set-v4l2
> >>>>>> '"dw-csi.0":0[fmt:SRGGB10_1X10/1920x1080]'
> >>>>>> media-ctl -d /dev/media0 --set-v4l2 '"csi2dc":0[fmt:SRGGB10_1X10/1920x1080]'
> >>>>>> media-ctl -d /dev/media0 --set-v4l2
> >>>>>> '"atmel_isc_scaler":0[fmt:SRGGB10_1X10/1920x1080]'
> >>>>>>
> >>>>>> Thank you for taking care of this !
> >>>>>>
> >>>>>> Eugen
> >>>>>>
> >>>>>>> Regards,
> >>>>>>>
> >>>>>>>            Hans
> >>>>>>>
> >>>>>>>>
> >>>>>>>> Full series history:
> >>>>>>>>
> >>>>>>>> Changes in v10:
> >>>>>>>> -> split the series into this first fixes part.
> >>>>>>>> -> moved IO_MC addition from first patch to the second patch on the driver changes
> >>>>>>>> -> edited commit messages
> >>>>>>>> -> DT nodes now disabled by default.
> >>>>>>>>
> >>>>>>>> Changes in v9:
> >>>>>>>> -> kernel robot reported isc_link_validate is not static, changed to static.
> >>>>>>>>
> >>>>>>>> Changes in v8:
> >>>>>>>> -> scaler: modified crop bounds to have the exact source size
> >>>>>>>>
> >>>>>>>> Changes in v7:
> >>>>>>>> -> scaler: modified crop bounds to have maximum isc size
> >>>>>>>> -> format propagation: did small changes as per Jacopo review
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Changes in v6:
> >>>>>>>> -> worked a bit on scaler, added try crop and other changes as per Jacopo review
> >>>>>>>> -> worked on isc-base enum_fmt , reworked as per Jacopo review
> >>>>>>>>
> >>>>>>>> Changes in v5:
> >>>>>>>> -> removed patch that removed the 'stop' variable as it was still required
> >>>>>>>> -> added two new trivial patches
> >>>>>>>> -> reworked some parts of the scaler and format propagation after discussions with Jacopo
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Changes in v4:
> >>>>>>>> -> as reviewed by Hans, added new patch to remove the 'stop' variable and reworked
> >>>>>>>> one patch that was using it
> >>>>>>>> -> as reviewed by Jacopo, reworked some parts of the media controller implementation
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Changes in v3:
> >>>>>>>> - change in bindings, small fixes in csi2dc driver and conversion to mc
> >>>>>>>> for the isc-base.
> >>>>>>>> - removed some MAINTAINERS patches and used patterns in MAINTAINERS
> >>>>>>>>
> >>>>>>>> Changes in v2:
> >>>>>>>> - integrated many changes suggested by Jacopo in the review of the v1 series.
> >>>>>>>> - add a few new patches
> >>>>>>>>
> >>>>>>>> Eugen Hristev (5):
> >>>>>>>>      media: atmel: atmel-isc: prepare for media controller support
> >>>>>>>>      media: atmel: atmel-isc: implement media controller
> >>>>>>>>      ARM: dts: at91: sama7g5: add nodes for video capture
> >>>>>>>>      ARM: configs: at91: sama7: add xisc and csi2dc
> >>>>>>>>      ARM: multi_v7_defconfig: add atmel video pipeline modules
> >>>>>>>>
> >>>>>>>>     arch/arm/boot/dts/sama7g5.dtsi                |  51 ++
> >>>>>>>>     arch/arm/configs/multi_v7_defconfig           |   3 +
> >>>>>>>>     arch/arm/configs/sama7_defconfig              |   2 +
> >>>>>>>>     drivers/media/platform/atmel/Makefile         |   2 +-
> >>>>>>>>     drivers/media/platform/atmel/atmel-isc-base.c | 485 +++++++++---------
> >>>>>>>>     .../media/platform/atmel/atmel-isc-scaler.c   | 267 ++++++++++
> >>>>>>>>     drivers/media/platform/atmel/atmel-isc.h      |  50 +-
> >>>>>>>>     .../media/platform/atmel/atmel-sama5d2-isc.c  |  34 +-
> >>>>>>>>     .../media/platform/atmel/atmel-sama7g5-isc.c  |  32 +-
> >>>>>>>>     9 files changed, 685 insertions(+), 241 deletions(-)
> >>>>>>>>     create mode 100644 drivers/media/platform/atmel/atmel-isc-scaler.c
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>
>