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   paulk-leonov: hi
   <br> I'm looking for a way to get per-frame status from the subdev, in the context of a camera
   <br> like, the camera has a status bit saying if it's correct or not
   <br> and I'd like to report that to the controller
   <br> I'm thinking that a control + a bottom half thread in the capture ISR to read that control from the subdev would do
   <br> but maybe there's a better way?
   sailus: paulk-leonov: Many receivers provide start of frame event which you can subscribe in user space.
   <br> Then you can read the control you're interested in.
   <br> If the start of frame is what you need, that is.
   <br> Other interrupts are end of frame or when the frame has been written to memory, but there's currently no event for this as it's commonly less needed and there's usually a related buffer available, too.
   paulk-leonov: <u>sailus</u>: I'm not sure what would be a good fit -- I also want to catch transmission errors
   <br> in practice I'm doing mipi csi-2 capture
   <br> <u>as</u>: CSI controller -- subdev --&gt; MIPI CSI-2 controller -- subdev --&gt; camera
   <br> and basically the mipi csi-2 controller has an interrupt that can report transmission errors or corruption
   <br> and I want to report that to "CSI controller" which sets the frame status
   sailus: paulk-leonov: Does your CSI-2 receiver driver manage the DMA, too?
   paulk-leonov: <u>sailus</u>: no, it's like an internal FIFO between the CSI-2 and the CSI controller (which does the dma)
   <br> <u>sailus</u>: at this point I'm considering V4L2_DEVICE_NOTIFY_EVENT with a custom event giving the status
   <br> to notify the controller of a rx error
   sailus: I think there are other drivers that could use this, too, so it'd be nice to generalise this somehow.
   <br> In most cases the CSI-2 receiver and the DMA are in one and the same device, but that's indeed not always the case.
   paulk-leonov: <u>sailus</u>: do you think an event-based mechanism would work?
   <br> I'm a bit worried about races between IRQs
   <br> and whether an erroneous frame will trigger an IRQ on the controller that does DMA or not
   hverkuil: <u>dafna2</u>: ping