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

[Laurent Pinchart]

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.

> [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