1NOTE:
2=====
3
4While the driver probes the hardware and reports itself as a
5V4L2 driver, there are still some issues preventing it to
6stream (at least it doesn't with the standard V4L2 applications.
7Didn't test yet with some custom-made app for this driver).
8Solving the related bugs and issues preventing it to work is
9needed (items 6 and 7 from the list below).
10
11TODO
12====
13
141. The atomisp doesn't rely at the usual i2c stuff to discover the
15   sensors. Instead, it calls a function from atomisp_gmin_platform.c.
16   There are some hacks added there for it to wait for sensors to be
17   probed (with a timeout of 2 seconds or so).
18   This should be converted to the usual way, using V4L2 async subdev
19   framework to wait for cameras to be probed;
20
212. Use ACPI _DSM table - DONE!
22
233. Switch the driver to use pm_runtime stuff. Right now, it probes the
24   existing PMIC code and sensors call it directly.
25
264. There's a problem at the sensor drivers: when trying to set a video
27   format, the atomisp main driver calls the sensor drivers with the
28   sensor turned off. This causes them to fail.
29
30   The only exception is the atomisp-ov2880, which has a hack inside it
31   to turn it on when VIDIOC_S_FMT is called.
32
33   The right fix seems to power on the sensor when a video device is
34   opened (or at the first VIDIOC_ ioctl - except for VIDIOC_QUERYCAP),
35   powering it down at close() syscall.
36
37   Such kind of control would need to be done inside the atomisp driver,
38   not at the sensors code.
39
405. There are several issues related to memory management, causing
41   crashes. The atomisp splits the memory management on three separate
42   regions:
43
44	- dynamic pool;
45	- reserved pool;
46	- generic pool
47
48   The code implementing it is at:
49
50	drivers/staging/media/atomisp/pci/hmm/
51
52   It also has a separate code for managing DMA buffers at:
53
54	drivers/staging/media/atomisp/pci/mmu/
55
56   The code there is really dirty, ugly and probably wrong. I fixed
57   one bug there already, but the best would be to just trash it and use
58   something else. Maybe the code from the newer intel driver could
59   serve as a model:
60
61	drivers/staging/media/ipu3/ipu3-mmu.c
62
63   But converting it to use something like that is painful and may
64   cause some breakages.
65
666. There is some issues at the frame receive logic, causing the
67   DQBUF ioctls to fail.
68
697. A single AtomISP driver needs to be implemented to support both
70   Baytrail (BYT) and Cherrytail (CHT) platforms at the same time.
71   The current driver is a mechanical and hand combined merge of the
72   two using several runtime macros, plus some ifdef ISP2401 to select the
73   CHT version. Yet, there are some ISP-specific headers that change the
74   driver's behavior during compile time.
75
768. The file structure needs to get tidied up to resemble a normal Linux
77   driver.
78
799. Lots of the midlayer glue. unused code and abstraction needs removing.
80
8110. The AtomISP driver includes some special IOCTLS (ATOMISP_IOC_XXXX_XXXX)
82    and controls that require some cleanup. Some of those code may have
83    been removed during the cleanups. They could be needed in order to
84    properly support 3A algorithms
85
86    Such IOCTL interface needs more documentation. The better would
87    be to use something close to the interface used by the IPU3 IMGU driver.
88
8911. The ISP code has some dependencies of the exact FW version.
90    The version defined in pci/sh_css_firmware.c:
91
92    BYT (isp2400): "irci_stable_candrpv_0415_20150521_0458"
93
94    CHT (isp2401): "irci_ecr - master_20150911_0724"
95
96    Those versions don't seem to be available anymore. On the tests we've
97    done so far, this version also seems to work for CHT:
98
99		"irci_stable_candrpv_0415_20150521_0458"
100
101    Which can be obtainable from Yocto Atom ISP respository.
102
103    but this was not thoroughly tested.
104
105    At some point we may need to round up a few driver versions and see if
106    there are any specific things that can be done to fold in support for
107    multiple firmware versions.
108
10912. Switch to standard V4L2 sub-device API for sensor and lens. In
110    particular, the user space API needs to support V4L2 controls as
111    defined in the V4L2 spec and references to atomisp must be removed from
112    these drivers.
113
11413. Use LED flash API for flash LED drivers such as LM3554 (which already
115    has a LED class driver).
116
11714. Switch from videobuf1 to videobuf2. Videobuf1 is being removed!
118
11915. Correct Coding Style. Please refrain sending coding style patches
120    for this driver until the other work is done, as there will be a lot
121    of code churn until this driver becomes functional again.
122
12316. Fix private ioctls to not need a compat_ioctl handler for running
124    32-bit tasks. The compat code has been removed because of bugs,
125    and should not be needed for modern drivers. Fixing this properly
126    unfortunately means an incompatible ABI change.
127
128Limitations
129===========
130
1311. To test the patches, you also need the ISP firmware
132
133   for BYT: /lib/firmware/shisp_2400b0_v21.bin
134   for CHT: /lib/firmware/shisp_2401a0_v21.bin
135
136   The firmware files will usually be found in /etc/firmware on an Android
137   device but can also be extracted from the upgrade kit if you've managed
138   to lose them somehow.
139
1402. Without a 3A library the capture behaviour is not very good. To take a good
141   picture, you need tune ISP parameters by IOCTL functions or use a 3A library
142   such as libxcam.
143
1443. The driver is intended to drive the PCI exposed versions of the device.
145   It will not detect those devices enumerated via ACPI as a field of the
146   i915 GPU driver.
147
148   There are some patches adding i915 GPU support floating at the Yocto's
149   Aero repository (so far, untested upstream).
150
1514. The driver supports only v2 of the IPU/Camera. It will not work with the
152   versions of the hardware in other SoCs.
153