media: imx-jpeg: Check decoding is ongoing for motion-jpeg

media: imx-jpeg: Check decoding is ongoing for motion-jpeg

As the first frame in "repeat-mode" is the pattern, the pattern done
interrupt is ignored by the driver. With small resolution bitstreams,
the interrupts might fire too quickly and hardware combine two irqs to
once because irq handle have latency. Thus the driver might miss the
frame decode done interrupt from the first actual frame.

In order to avoid the driver wait for the frame done interrupt that has
been combined to the pattern done interrupt and been ignored, driver
will check the curr_desc and slot_status registers to figure out if the
decoding of actual frame is finished or not.

Firstly we check the curr_desc register,
- if it is still pointing to the pattern descriptor, the second actual
frame is not started, we can wait for its frame-done interrupt.
- if the curr_desc has pointed to the frame descriptor, then we check the
ongoing bit of slot_status register.
- if the ongoing bit is set to 1, the decoding of the actual frame is not
finished, we can wait for its frame-done interrupt.
- if the ongoing bit is set to 0, the decoding of the actual frame is
finished, we can't wait for the second interrupt, but mark it as done.

But there is still a small problem, that the curr_desc and slot_status
registers are not synchronous. curr_desc is updated when the
next_descpt_ptr is loaded, but the ongoing bit of slot_status is set
after the 32 bytes descriptor is loaded, there will be a short time
interval in between, which may cause fake false. Consider read register
is quite slow compared with IP read 32byte from memory, read twice
slot_status can avoid this situation.

Signed-off-by: Ming Qian <ming.qian@oss.nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>