media: rkisp1: Improve frame sequence correctness on stats and params buffers

media: rkisp1: Improve frame sequence correctness on stats and params buffers

On the rkisp1 (in my case on a NXP i.MX8 M Plus) the ISP interrupt
handler is sometimes called with RKISP1_CIF_ISP_V_START (start of frame)
and RKISP1_CIF_ISP_FRAME (end of frame) being set at the same time. In
commit 8524fa22fd2f ("media: staging: rkisp1: isp: add a warning and
debugfs var for irq delay") a warning was added for that. There are two
cases where this condition can occur:

1. The v-sync and the frame-end belong to the same frame. This means,
   the irq was heavily delayed and the warning is likely appropriate.

2. The v-sync belongs to the next frame. This can happen if the vertical
   blanking between two frames is very short.

The current code always handles case 1 although case 2 is in my
experience the more common case and happens in regular usage. This leads
to incorrect sequence numbers on stats and params buffers which in turn
breaks the regulation in user space. Fix that by adding a frame_active
flag to distinguish between these cases and handle the start of frame
either at the beginning or at the end of the rkisp1_isp_isr().

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Link: https://patch.msgid.link/20250922182003.3712101-2-stefan.klug@ideasonboard.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>