Message-ID: <20201105145821.GC615923@aptenodytes>
Date:   Thu, 5 Nov 2020 15:58:21 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Helen Koike <helen.koike@...labora.com>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-sunxi@...glegroups.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Yong Deng <yong.deng@...ewell.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Hans Verkuil <hverkuil@...all.nl>, kevin.lhopital@...mail.com
Subject: Re: [PATCH 00/14] Allwinner MIPI CSI-2 support for A31/V3s/A83T

Hi,

On Wed 04 Nov 20, 13:36, Helen Koike wrote:
> Hi Paul,
> 
> On 11/4/20 8:11 AM, Paul Kocialkowski wrote:
> > Hi Helen,
> > 
> > On Fri 30 Oct 20, 19:44, Helen Koike wrote:
> >> Hi Paul,
> >>
> >> I have some comments through the series, I hope this helps.
> > 
> > Thanks for your comments :)
> > 
> >> On 10/23/20 2:45 PM, Paul Kocialkowski wrote:
> >>> This series introduces support for MIPI CSI-2, with the A31 controller that is
> >>> found on most SoCs (A31, V3s and probably V5) as well as the A83T-specific
> >>> controller. While the former uses the same MIPI D-PHY that is already supported
> >>> for DSI, the latter embeds its own D-PHY.
> >>>
> >>> In order to distinguish the use of the D-PHY between Rx mode (for MIPI CSI-2)
> >>> and Tx mode (for MIPI DSI), a submode is introduced for D-PHY in the PHY API.
> >>> This allows adding Rx support in the A31 D-PHY driver.
> >>>
> >>> A few changes and fixes are applied to the A31 CSI controller driver, in order
> >>> to support the MIPI CSI-2 use-case.
> >>>
> >>> Follows is the V4L2 device topology representing the interactions between
> >>> the MIPI CSI-2 sensor, the MIPI CSI-2 controller (which controls the D-PHY)
> >>> and the CSI controller:
> >>> - entity 1: sun6i-csi (1 pad, 1 link)
> >>>             type Node subtype V4L flags 0
> >>>             device node name /dev/video0
> >>> 	pad0: Sink
> >>> 		<- "sun6i-mipi-csi2":1 [ENABLED,IMMUTABLE]
> >>>
> >>> - entity 5: sun6i-mipi-csi2 (2 pads, 2 links)
> >>>             type V4L2 subdev subtype Unknown flags 0
> >>> 	pad0: Sink
> >>> 		<- "ov5648 0-0036":0 [ENABLED,IMMUTABLE]
> >>> 	pad1: Source
> >>> 		-> "sun6i-csi":0 [ENABLED,IMMUTABLE]
> >>>
> >>> - entity 8: ov5648 0-0036 (1 pad, 1 link)
> >>>             type V4L2 subdev subtype Sensor flags 0
> >>>             device node name /dev/v4l-subdev0
> >>
> >> Question: I noticed is that sun6i-mipi-csi2 doesn't expose a node under /dev/, but the sensor
> >> exposes it. Probably because it uses V4L2_SUBDEV_FL_HAS_DEVNODE and sun6i-csi() calls
> >> v4l2_device_register_subdev_nodes().
> >>
> >> I find this weird from a userspace pov, since usually we don't mix manual and auto propagation
> >> of the configs, so I started wondering if sun6i-csi driver should be calling
> >> v4l2_device_register_subdev_nodes() in the first place.
> > 
> > I must admit that I didn't really pay attention to that, but since
> > sun6i-mipi-csi2 is basically a bridge driver, it doesn't make sense to apply
> > manual configuration to it. It is actually designed to forward most subdev ops
> > to its own subdev so configuring it manually would actually result in
> > configuring the sensor.
> 
> Ack, then maybe sun6i-csi needs a patch removing the call to v4l2_device_register_subdev_nodes()

Apparently Sakari suggested that we do need a subdev node for the MIPI CSI-2
bridge so I'll just do that.

This implementation that fowards the ops to the sensor was apparently a mistake.

Paul

> > 
> > XXX
> > 
> >> Also, sun6i-csi doesn't seem to be used by any board dts (it's declared on the dtsi, but I
> >> didn't find any dts enabling it), so I wonder if it would be a bad thing if we update it.
> >>
> >>> 	pad0: Source
> >>> 		[fmt:SBGGR8_1X8/640x480@...0 field:none colorspace:raw xfer:none ycbcr:601 quantization:full-range]
> >>> 		-> "sun6i-mipi-csi2":0 [ENABLED,IMMUTABLE]
> >>
> >> If I understand correctly, this is very similar to ipu3:
> >>     sensor->bus->dma_engine
> >>
> >> in the case of ipu3-cio2:
> >>     sensor->ipu3-csi2->ipu3-cio2
> >>
> >> in this case:
> >>     ov5648->sun6i-mipi-csi2->sun6i-csi
> > 
> > Yes this is the correct picture.
> > 
> >> On thing that is confusing me is the name csi2 with csi (that makes me think of csi
> >> version one, which is not the case), I would rename it to sun6i-video (or maybe
> >> it is just me who gets confused).
> > 
> > So the CSI name comes from the Allwinner litterature and implementation for that
> > controller. Since it supports parallel input on its own, it does in fact support
> > parallel CSI. The DMA engine part alone from that controller is also used for
> > MIPI CSI-2, so in this case the name looses its relevance.
> > 
> >> I know this driver is already upstream and not part of this series, but on the other hand it
> >> doesn't seem to be used.
> > 
> > Personally I don't find a rename to be necessary and while I agree that
> > nothing would apparently prevent us from renaming it, I would prefer to keep
> > the naming in line with Allwinner's litterature.
> 
> Ok, I didn't know it was from Allwinner's litterature, I don't mind keeping the name.

Great :)

> >> On another note, I always wonder if we should expose the bus in the topology, I'm not
> >> sure if it provides any useful API or information for userspace, and you could have
> >> a cleaner code (maybe code could be under phy subsystem). But at the same time, it
> >> seems this is a pattern on v4l2.
> >>
> >> I'd like to hear what others think on the above.
> > 
> > My view on this is that we are dealing with two distinct controllers here,
> > one that acts as a DMA engine and one that acts as a bridge. As a result, two
> > chained subdevs looks like the most appropriate representation to me.
> > 
> > Using the PHY subsystem would probably be abusing the framework since the
> > MIPI CSI-2 controller is not a PHY (and we do have a D-PHY driver for the D-PHY
> > part that uses the PHY API already).
> > 
> > So tl;dr I don't agree that it would be cleaner.
> 
> My point is, this is a "dummy" subdevice in userspace pov,
> but if it is only used with auto-propagation of the configurations, then
> it doesn't matter (since userspace won't interact with that node).
> And in the kernel space you need to implement media boilerplate code.
> So I was trying to think in another alternative, but tbh I don't mind
> keeping it in the media topology.

Undestood and thanks for sharing your thoughts either way, they are definitely
welcome!

Cheers,

Paul

> Regards,
> Helen
> 
> > 
> > Cheers,
> > 
> > Paul
> > 
> >>> Happy reviewing!
> >>>
> >>> Paul Kocialkowski (14):
> >>>   phy: Distinguish between Rx and Tx for MIPI D-PHY with submodes
> >>>   phy: allwinner: phy-sun6i-mipi-dphy: Support D-PHY Rx mode for MIPI
> >>>     CSI-2
> >>>   media: sun6i-csi: Support an optional dedicated memory pool
> >>>   media: sun6i-csi: Fix the image storage bpp for 10/12-bit Bayer
> >>>     formats
> >>>   media: sun6i-csi: Only configure the interface data width for parallel
> >>>   media: sun6i-csi: Support feeding from the MIPI CSI-2 controller
> >>>   dt-bindings: media: i2c: Add A31 MIPI CSI-2 bindings documentation
> >>>   media: sunxi: Add support for the A31 MIPI CSI-2 controller
> >>>   ARM: dts: sun8i: v3s: Add CSI0 camera interface node
> >>>   ARM: dts: sun8i: v3s: Add MIPI D-PHY and MIPI CSI-2 interface nodes
> >>>   dt-bindings: media: i2c: Add A83T MIPI CSI-2 bindings documentation
> >>>   media: sunxi: Add support for the A83T MIPI CSI-2 controller
> >>>   ARM: dts: sun8i: a83t: Add MIPI CSI-2 controller node
> >>>   media: sunxi: sun8i-a83t-mipi-csi2: Avoid using the (unsolicited)
> >>>     interrupt
> >>>
> >>>  .../media/allwinner,sun6i-a31-mipi-csi2.yaml  | 168 +++++
> >>>  .../media/allwinner,sun8i-a83t-mipi-csi2.yaml | 158 +++++
> >>>  arch/arm/boot/dts/sun8i-a83t.dtsi             |  26 +
> >>>  arch/arm/boot/dts/sun8i-v3s.dtsi              |  62 ++
> >>>  drivers/media/platform/sunxi/Kconfig          |   2 +
> >>>  drivers/media/platform/sunxi/Makefile         |   2 +
> >>>  .../platform/sunxi/sun6i-csi/sun6i_csi.c      |  54 +-
> >>>  .../platform/sunxi/sun6i-csi/sun6i_csi.h      |  20 +-
> >>>  .../platform/sunxi/sun6i-mipi-csi2/Kconfig    |  11 +
> >>>  .../platform/sunxi/sun6i-mipi-csi2/Makefile   |   4 +
> >>>  .../sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c   | 635 +++++++++++++++++
> >>>  .../sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.h   | 116 +++
> >>>  .../sunxi/sun8i-a83t-mipi-csi2/Kconfig        |  11 +
> >>>  .../sunxi/sun8i-a83t-mipi-csi2/Makefile       |   4 +
> >>>  .../sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.c    |  92 +++
> >>>  .../sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.h    |  39 ++
> >>>  .../sun8i_a83t_mipi_csi2.c                    | 660 ++++++++++++++++++
> >>>  .../sun8i_a83t_mipi_csi2.h                    | 196 ++++++
> >>>  drivers/phy/allwinner/phy-sun6i-mipi-dphy.c   | 164 ++++-
> >>>  drivers/staging/media/rkisp1/rkisp1-isp.c     |   3 +-
> >>>  include/linux/phy/phy-mipi-dphy.h             |  13 +
> >>>  21 files changed, 2408 insertions(+), 32 deletions(-)
> >>>  create mode 100644 Documentation/devicetree/bindings/media/allwinner,sun6i-a31-mipi-csi2.yaml
> >>>  create mode 100644 Documentation/devicetree/bindings/media/allwinner,sun8i-a83t-mipi-csi2.yaml
> >>>  create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/Kconfig
> >>>  create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/Makefile
> >>>  create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.c
> >>>  create mode 100644 drivers/media/platform/sunxi/sun6i-mipi-csi2/sun6i_mipi_csi2.h
> >>>  create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/Kconfig
> >>>  create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/Makefile
> >>>  create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.c
> >>>  create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_dphy.h
> >>>  create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.c
> >>>  create mode 100644 drivers/media/platform/sunxi/sun8i-a83t-mipi-csi2/sun8i_a83t_mipi_csi2.h
> >>>
> > 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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