media: atomisp: update TODO list

Let's reflect the current status at the TODO list, as other
developers can help addressing issues over there.
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/staging/media/atomisp/TODO

-1. A single AtomISP driver needs to be implemented to support both
-   Baytrail (BYT and Cherrytail (CHT) platforms at the same time.
+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. Support for newer board-specific data (like Asus T101HA support) uses a
+   DMI match table to retrieve sensor's data, using hard-coded values.
+   It sounds feasible to retrieve those data directly from ACPI via _DSM
+   tables (like this one, associated with CAM1 at the above mentioned
+   hardware):
+
+            Name (C1CD, Buffer (0x0220){})
+            Method (_DSM, 4, NotSerialized)  // _DSM: Device-Specific Method
+            {
+                If ((Arg0 == ToUUID ("dc2f6c4f-045b-4f1d-97b9-882a6860a4be")))
+                {
+                    Local0 = Package (0x12)
+                        {
+                            "CamId",
+                            "ov2680",
+                            "CamType",
+                            "1",
+                            "CsiPort",
+                            "0",
+                            "CsiLanes",
+                            "1",
+                            "CsiFmt",
+                            "15",
+                            "CsiBayer",
+                            "0",
+                            "CamClk",
+                            "1",
+                            "Regulator1p8v",
+                            "0",
+                            "Regulator2p8v",
+                            "0"
+                        }
+                    Return (Local0)
+                }
+
+   The code there at atomisp_gmin_platform has an EFI parser, but it
+   assumes that the information would be stored on a different way.
+
+   As the Kernel has support for reading data from _DSM, via
+   acpi_evaluate_dsm(), it sounds doable to use such infra and remove the
+   DMI match, at least for some devices. This will likely allow covering
+   more devices that could also be using the same EFI UUID.
+
+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.
 
-2. The file structure needs to get tidied up to resemble a normal Linux
+8. The file structure needs to get tidied up to resemble a normal Linux
    driver.
 
-3. Lots of the midlayer glue. unused code and abstraction needs removing.
+9. Lots of the midlayer glue. unused code and abstraction needs removing.
 
-3. The sensor drivers read MIPI settings from EFI variables or default to the
-   settings hard-coded in the platform data file for different platforms.
-   It should be possible to improve it, by adding support for _DSM tables.
+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
 
-4. The sensor drivers use PMIC and the regulator framework API. In the ideal
-   world it would be using ACPI but that's not how the existing devices work.
+    Such IOCTL interface needs more documentation. The better would
+    be to use something close to the interface used by the IPU3 IMGU driver.
 
-5. The AtomISP driver includes some special IOCTLS (ATOMISP_IOC_XXXX_XXXX)
-   and controls that require some cleanup.
+11. The ISP code has some dependencies of the exact FW version.
+    The version defined in pci/sh_css_firmware.c:
 
-6. Correct Coding Style. Please don't send coding style patches for this
-   driver until the other work is done.
+    BYT (isp2400): "irci_stable_candrpv_0415_20150521_0458"
 
-7. The ISP code has some dependencies of the exact FW version.
-   The version defined in pci/sh_css_firmware.c:
-   BYT:
-	static const char *isp2400_release_version = STR(irci_stable_candrpv_0415_20150521_0458);
+    CHT (isp2401): "irci_ecr - master_20150911_0724"
 
-   CHT:
-	static const char *isp2401_release_version = STR(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:
 
-   Those versions don't seem to be available anymore. On the tests we've
-   done so far, this version also seems to work for isp2401:
+		"irci_stable_candrpv_0415_20150521_0458"
 
-		irci_stable_candrpv_0415_20150521_0458
+    Which can be obtainable from Yocto Atom ISP respository.
 
-   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.
+    but this was not thoroughly tested.
 
-8. Switch to V4L2 async API to set up sensor, lens and flash devices.
-   Control those devices using V4L2 sub-device API without custom
-   extensions.
+    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.
 
-9. 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.
+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.
 
-10. Use LED flash API for flash LED drivers such as LM3554 (which already
+13. Use LED flash API for flash LED drivers such as LM3554 (which already
     has a LED class driver).
 
-11. Switch from videobuf1 to videobuf2. Videobuf1 is being removed!
+14. Switch from videobuf1 to videobuf2. Videobuf1 is being removed!
 
-12. There are some memory management code that seems to be
-    forked from Kernel 3.10 inside hmm/ directory. Get rid of it,
-    making the driver to use a more standard memory management module.
+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.
 
-13. 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.
-
-Limitations:
+Limitations
+===========
 
 1. To test the patches, you also need the ISP firmware
 
@@ -84,6 +181,8 @@ Limitations:
    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.
-