Hi Steve,
On Fri, 2021-01-08 at 11:10 -0800, Steve Longerbeam wrote:
>
> On 12/29/20 2:31 AM, Ezequiel Garcia wrote:
> > Currently, the CSI2 subdevice is using the data-lanes from the
> > neareast endpoint to config the CSI2 lanes.
> >
> > While this may work, the proper way to configure the hardware is
> > to obtain the remote subdevice in v4l2_async_notifier_operations.bound(),
> > and then call get_mbus_config using the remote subdevice to get
> > the active lanes.
> >
> > Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
> > ---
> > drivers/staging/media/imx/TODO | 12 ---
> > drivers/staging/media/imx/imx6-mipi-csi2.c | 101 ++++++++++++++++++---
> > 2 files changed, 90 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/staging/media/imx/TODO b/drivers/staging/media/imx/TODO
> > index 9cfc1c1e78dc..c575f419204a 100644
> > --- a/drivers/staging/media/imx/TODO
> > +++ b/drivers/staging/media/imx/TODO
> > @@ -2,18 +2,6 @@
> > - The Frame Interval Monitor could be exported to v4l2-core for
> > general use.
> >
> > -- The CSI subdevice parses its nearest upstream neighbor's device-tree
> > - bus config in order to setup the CSI. Laurent Pinchart argues that
> > - instead the CSI subdev should call its neighbor's g_mbus_config op
> > - (which should be propagated if necessary) to get this info. However
> > - Hans Verkuil is planning to remove the g_mbus_config op. For now this
> > - driver uses the parsed DT bus config method until this issue is
> > - resolved.
>
> This TODO was actually referring to the fwnode endpoint parsing in
> imx-media-csi.c, not imx6-mipi-csi2.c.
>
Ah, OK.
> But the same conversion to call .get_mbus_config() instead of endpoint
> parsing could be done in imx-media-csi.c, but there is one imx6
> constraint that is preventing this from happening. The imx6 reference
> manual states that if the CSI is receiving from an input parallel bus
> that is 16-bits wide, the data must go directly to memory via the SMFC
> and not be sent to the IPU's Image Converter ("passthrough" mode):
>
> "37.4.3.9 16 bit camera support
>
> Devices that support 16 bit data bus can be connected to the CSI. This
> can be done in one
> of the following ways.
>
> 16 bit YUV422
> In this mode the CSI receives 2 components per cycle. The CSI is
> programmed to
> accept the data as 16 bit generic data. The captured data will be stored
> in the memory
> through the SMFC. The IDMAC needs to be programmed to store 16bit
> generic data.
> When the data is read back from the memory for further processing in the
> IPU it will
> be read as YUV422 data."
>
> Same is said for RGB data to the CSI.
>
> I'm not sure if this restriction is real or not. If this restriction
> were ignored, the fwnode endpoint check "ep->bus.parallel.bus_width >=
> 16" could be removed and the only remaining info required to determine
> passthrough mode is available from 'struct v4l2_mbus_config' and the
> input mbus codes, thus allowing the conversion to .get_mbus_config().
>
For the sound of this, the above doesn't affect this patch, right?
Also, note there's a v2 submitted:
https://patchwork.linuxtv.org/project/linux-media/patch/20210103154155.318300-1-ezequiel@xxxxxxxxxxxxx/
Now, there's something I'm not exactly sure about these .get_mbus_config
conversions, being described in the TODO file.
The TODO file should only list what's missing to move the driver
out of staging. Converting to newer APIs doesn't seem a blocker:
there are a ton of drivers using old APIs out there, which is
a natural consequence of how the kernel evolve APIs all the time.
I'm wondering if the other TODO items apply as well, moving
the Frame Interval Monitor to the v4l2-core is something we
can always do at any later point. It shouldn't be a requirement
for destaging.
There's one thing that we must resolve before de-staging.
The media controller topology, which is a form of ABI should
be settled, as that's difficult to change later.
However, this item is not mentioned in the TODO.
So, I was thinking we should remove all the current TODO
items and add something about the media controller topology
stability requirements.
What do you think?
Cheers,
Ezequiel
