On Wed, Jul 12, 2023 at 04:55:21PM +0200, Paul Kocialkowski wrote: > On Fri 02 Jun 23, 13:03, Laurent Pinchart wrote: > > On Fri, Jun 02, 2023 at 11:39:54AM +0200, Paul Kocialkowski wrote: > > > Hi, > > > > > > (Re-adding folks from the original email, adding Laurent and Hans.) > > > > > > On Fri 02 Jun 23, 11:24, Martijn Braam wrote: > > > > Hi Paul, > > > > > > > > That's basically it yes. My software doesn't expect the bridge block, > > > > because it wasn't there. The pipeline always worked "automatically". > > > > > > > > This is the workaround that's been made now it run on newer kernels: > > > > https://gitlab.com/postmarketOS/megapixels/-/merge_requests/31 > > > > > > > > I'm pretty sure format propagation would fix this issue. > > > > > > Okay that's good to know. > > > > > > To be honest it's still not very clear to me if in-driver format propagation is > > > a "nice to have" feature or something that all media pipeline drivers are > > > supposed to implement. > > > > For MC-based drivers, in-kernel propagation *inside* subdevs is > > mandatory, in-kernel propagration *between* subdevs is not allowed. The > > latter is the responsibility of userspace. > > Right, makes good sense. > > > For traditional (I'd say legacy, but I know not everybody likes that > > term :-)) drivers that only expose video device nodes and do not expose > > subdev nodes to userspace, the driver is responsible for configuring the > > full pipeline internally based on the S_FMT call on the video nodes > > only. This isn't applicable to the sun6i-csi driver, as it exposes > > subdev nodes to userspace. > > > > > Anyway I feel like this is not really a regression but a result of the driver > > > being converted to a newer API. > > > > > > Also there's a V4L2_CAP_IO_MC flag which should indicate that the video device > > > must be controlled via the media controller API instead of being > > > video-device-centric, but I've seen comments asking not to set the flag even > > > when MC is used so I'm a bit confused here. > > > > Would you have pointers to those comments ? > > I was thinking of a reply from Hans on the Tegra driver series: > https://patchwork.kernel.org/project/linux-media/patch/20230309144320.2937553-4-luca.ceresoli@xxxxxxxxxxx/#25285456 > > From what I understand there's some bridge entity that needs to be explicitly > configured to match the sensor's format via MC, yet the reply says that the > driver "doesn't use the media controller for anything at the moment" and > should not be converted to become a proper MC-driven device. > > Well maybe there was a misunderstanding on my side, or Hans', or both. It makes sense not to set the flag in some cases. For instance, the uvcvideo driver creates an MC device to expose the camera's internal topology to userspace, but doesn't create subdevs as the UVC protocol doesn't allow fine-grained configuration of formats between entities. In the sun6i-csi case, I don't think this is applicable, the device should be configured directly at the subdev level by userspace as you can't know in advance what will be connected to its inputs. For what it's worth, the same reasoning should apply to the tegra driver, and I think it should set V4L2_CAP_IO_MC. > > > Perhaps the flag is only required when there is no automatic format > > > propagation? > > > > The flag is more or less required when you expose subdev nodes to > > userspace. > > Thanks for the clarifications :) > > > > If anyone has solid answers on these points I'd be happy to read some > > > clarification (and act accordingly). > > > > > > > On 6/2/23 11:16, Paul Kocialkowski wrote: > > > > > Hi Martijn, > > > > > > > > > > On Thu 01 Jun 23, 23:19, Martijn Braam wrote: > > > > > > It seems like this commit: > > > > > > > > > > > > media: sun6i-csi: Add bridge v4l2 subdev with port management > > > > > > > > > > > > Has changed the way the media pipeline on a64 devices, in my case the PINE64 > > > > > > PinePhone works. Since this is an API towards userspace and there's active > > > > > > applications that use it I think this counts as a regression. > > > > > Do you have more details on what changed specifically? > > > > > > > > > > The commit added a bridge subdev in addition to the video node, which is > > > > > generally a better description of the CSI hardware and also a necessity > > > > > to support the ISP data flow. > > > > > > > > > > Maybe your userspace application is not configuring the bridge media block with > > > > > the right format, which results in a mismatch? > > > > > > > > > > Some work was started to achieve automatic format propagation, perhaps it > > > > > would be enough to solve your issue. > > > > > > > > > > Cheers, > > > > > > > > > > Paul > > > > > > > > > > > #regzbot introduced: 0d2b746b1bef73de62d2d311e594a7ffed4ca43 -- Regards, Laurent Pinchart
