NOTE:
=====

While the driver probes the hardware and reports itself as a
V4L2 driver, there are still some issues preventing it to
stream (at least it doesn't with the standard V4L2 applications.
Didn't test yet with some custom-made app for this driver).
Solving the related bugs and issues preventing it to work is
needed (items 6 and 7 from the list below).

TODO
====

1. The atomisp doesn't rely at the usual i2c stuff to discover the
   sensors. Instead, it calls a function from atomisp_gmin_platform.c.
   There are some hacks added there for it to wait for sensors to be
   probed (with a timeout of 2 seconds or so).
   This should be converted to the usual way, using V4L2 async subdev
   framework to wait for cameras to be probed;

2. Use ACPI _DSM table - DONE!

3. Switch the driver to use pm_runtime stuff. Right now, it probes the
   existing PMIC code and sensors call it directly.

4. There's a problem at the sensor drivers: when trying to set a video
   format, the atomisp main driver calls the sensor drivers with the
   sensor turned off. This causes them to fail.

   The only exception is the atomisp-ov2880, which has a hack inside it
   to turn it on when VIDIOC_S_FMT is called.

   The right fix seems to power on the sensor when a video device is
   opened (or at the first VIDIOC_ ioctl - except for VIDIOC_QUERYCAP),
   powering it down at close() syscall.

   Such kind of control would need to be done inside the atomisp driver,
   not at the sensors code.

5. There are several issues related to memory management, causing
   crashes. The atomisp splits the memory management on three separate
   regions:

	- dynamic pool;
	- reserved pool;
	- generic pool

   The code implementing it is at:

	drivers/staging/media/atomisp/pci/hmm/

   It also has a separate code for managing DMA buffers at:

	drivers/staging/media/atomisp/pci/mmu/

   The code there is really dirty, ugly and probably wrong. I fixed
   one bug there already, but the best would be to just trash it and use
   something else. Maybe the code from the newer intel driver could
   serve as a model:

	drivers/staging/media/ipu3/ipu3-mmu.c

   But converting it to use something like that is painful and may
   cause some breakages.

6. There is some issues at the frame receive logic, causing the
   DQBUF ioctls to fail.

7. A single AtomISP driver needs to be implemented to support both
   Baytrail (BYT) and Cherrytail (CHT) platforms at the same time.
   The current driver is a mechanical and hand combined merge of the
   two using several runtime macros, plus some ifdef ISP2401 to select the
   CHT version. Yet, there are some ISP-specific headers that change the
   driver's behavior during compile time.

8. The file structure needs to get tidied up to resemble a normal Linux
   driver.

9. Lots of the midlayer glue. unused code and abstraction needs removing.

10. The AtomISP driver includes some special IOCTLS (ATOMISP_IOC_XXXX_XXXX)
    and controls that require some cleanup. Some of those code may have
    been removed during the cleanups. They could be needed in order to
    properly support 3A algorithms

    Such IOCTL interface needs more documentation. The better would
    be to use something close to the interface used by the IPU3 IMGU driver.

11. The ISP code has some dependencies of the exact FW version.
    The version defined in pci/sh_css_firmware.c:

    BYT (isp2400): "irci_stable_candrpv_0415_20150521_0458"

    CHT (isp2401): "irci_ecr - master_20150911_0724"

    Those versions don't seem to be available anymore. On the tests we've
    done so far, this version also seems to work for CHT:

		"irci_stable_candrpv_0415_20150521_0458"

    Which can be obtainable from Yocto Atom ISP respository.

    but this was not thoroughly tested.

    At some point we may need to round up a few driver versions and see if
    there are any specific things that can be done to fold in support for
    multiple firmware versions.

12. Switch to standard V4L2 sub-device API for sensor and lens. In
    particular, the user space API needs to support V4L2 controls as
    defined in the V4L2 spec and references to atomisp must be removed from
    these drivers.

13. Use LED flash API for flash LED drivers such as LM3554 (which already
    has a LED class driver).

14. Switch from videobuf1 to videobuf2. Videobuf1 is being removed!

15. Correct Coding Style. Please refrain sending coding style patches
    for this driver until the other work is done, as there will be a lot
    of code churn until this driver becomes functional again.

16. Fix private ioctls to not need a compat_ioctl handler for running
    32-bit tasks. The compat code has been removed because of bugs,
    and should not be needed for modern drivers. Fixing this properly
    unfortunately means an incompatible ABI change.

Limitations
===========

1. To test the patches, you also need the ISP firmware

   for BYT: /lib/firmware/shisp_2400b0_v21.bin
   for CHT: /lib/firmware/shisp_2401a0_v21.bin

   The firmware files will usually be found in /etc/firmware on an Android
   device but can also be extracted from the upgrade kit if you've managed
   to lose them somehow.

2. Without a 3A library the capture behaviour is not very good. To take a good
   picture, you need tune ISP parameters by IOCTL functions or use a 3A library
   such as libxcam.

3. The driver is intended to drive the PCI exposed versions of the device.
   It will not detect those devices enumerated via ACPI as a field of the
   i915 GPU driver.

   There are some patches adding i915 GPU support floating at the Yocto's
   Aero repository (so far, untested upstream).

4. The driver supports only v2 of the IPU/Camera. It will not work with the
   versions of the hardware in other SoCs.