Hi Laurent,
thank you for your comprehensive answer.
On 25.04.20 04:39, Laurent Pinchart wrote:
Hi Patrik,
(CC'ing Sakari Ailus)
On Sat, Apr 18, 2020 at 04:39:25PM +0200, Patrik Gfeller wrote:
Hello Mauro et al,
I've recently switched to Linux, and I'm very impressed. Almost
everything thing works out of the box. Only the webcam on my device does
not. I did some digging and if I'm right an atomisp driver would be
required. Is this correct? Below the output of lspci:
00:00.0 Host bridge: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series SoC Transaction Register (rev 36)
00:02.0 VGA compatible controller: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Integrated Graphics Controller (rev 36)
00:03.0 Multimedia controller: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series Imaging Unit (rev 36)
00:0a.0 Non-VGA unclassified device: Intel Corporation Device 22d8 (rev 36)
00:0b.0 Signal processing controller: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series Power Management Controller (rev 36)
00:14.0 USB controller: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series USB xHCI Controller (rev 36)
00:1a.0 Encryption controller: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series Trusted Execution Engine (rev 36)
00:1c.0 PCI bridge: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series PCI Express Port #1 (rev 36)
00:1f.0 ISA bridge: Intel Corporation Atom/Celeron/Pentium Processor x5-E8000/J3xxx/N3xxx Series PCU (rev 36)
01:00.0 Network controller: Qualcomm Atheros QCA9377 802.11ac Wireless Network Adapter (rev 31)
According to the history it looks like the driver was removed from the
kernel in 2018 and replaced with a dummy driver (to make sure power save
works).
Is there a chance that the atomisp driver will return to the kernel?
As much as I'd like to say yes, I think this is unfortunately very
unlikely. There are a few obstacles to getting a working camera with
atomisp:
- According to some reports, the driver doesn't work. That's the first
thing that would need to be fixed, and without hardware documentation
and support from Intel, that would be a difficult (to say the least)
task.
- Assuming we could fix the driver, we would need to make sure it
supports your device. If the atomisp is anything like the IPU3 (a more
recent ISP from Intel), there are two different and incompatible sets
of ACPI data formats related to the device, one developed for Windows,
and one developed for Linux. I expect the atomisp driver to support
the latter but not the former. If your device was shipped with
Windows, it uses the Windows-specific ACPI data format. Furthermore,
it would in that case likely not encode all the information we would
need in ACPI, as Windows drivers have the bad habit of hardcoding
device-specific data in drivers. At the very least we would need to
get the atomisp to support the Windows ACPI data format (which is most
likely completely undocumented), and we would need to figure out how
to retrieve data that are simply not there. This being said, maybe the
atomisp ACPI design was better than the IPU3 and all (or part of)
those issues don't exist, but I'd be surprised.
- At this point you would (hopefully) have a driver that could capture
RAW images. In order to use the camera as a webcam, those images would
need to be processed by the ISP that is part of the atomisp. This
requires complex image processing algorithm control code in userspace.
Intel has not released any open version of such code for the atomisp
(or any other platform) to my knowledge, so this would need to be
implemented from scratch. The libcamera project could help there, as
it provides a framework to host such code, but the atomisp-specific
code would still need to be implemented. This is a complex task when
the hardware is fully documented, without hardware documentation and
thus without knowing how the hardware works, it gets extremely
difficult. The task would be orders of magnitude more complex than
reverse-engineering a GPU.
- Finally, in order for the driver to be merged back in the upstream
kernel, it would require massive cleanups, but that's the simplest
task of all that is required here.
I'm sorry for the bad news, we need to be more vocal blaming hardware
vendors for this type of mess.
Bad news indeed, this doesn't sound promising at all. I can confirm that
the driver does not work out of the box in its current state (many
thanks to Mauro for making this test possible). With all those obstacles
I'm surprised that work on such a driver was even started. My only hope
is, that the ISP 2 is better documented and less complex than ISP 3 ...
I'll try to get hold of hardware documentation from Intel, and check if
there is any kind of community support program in place (it is at least
worth a try :-) ) - that hopefully would allow to assess if there is a
possibility to fix the driver and how much post processing would be
needed in user space (what raw format that thing delivers).
Unfortunately I would depend on others to do the judgment (I do not have
the technical skills necessary). I'll also try to find out who initiated
the original implementation to find out on what documentation it was
based (or if it was all reverse engineering) and what was the rational
to asses such an implementation as possible.
What I've found already is a public document about the ISP2-Registers of
the x5-Z8350:
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/atom-z8000-datasheet-vol-2.pdf
(page 972 ff.) - not sure if this is of any help.
What kind of documentation would be needed? What I understood so far is
that details of ACPI format are important.
As already mentioned: I would also sponsor a device or two to developers
with a reputation as you and Mauro have (preferably the same device I
have :-), they are quite cheap today - and that is a way I could support
the efforts).
There are quite a few older tablets and 2in1 devices that would benefit.
Unfortunately I do not understand the removed code (my coding skills are
very basic) and can thus not help to change what ever is necessary to
make it fit for the kernel :-( (does not sound like a beginner project).
However - I would be glad to help out to help testing an ISP driver.
However - even without the cam it is a very impressing operating system
which I enjoy very much. I would like to thank all of you for your work
that benefits so many people!
You're welcome. Your thanks are much appreciated :-)
with kind regards,
Patrik
