Re: cio2 ipu3 module to automatically connect sensors via swnodes

[Kieran Bingham <kieran.bingham@ideasonboard.com>]

Hi Daniel,

On 07/09/2020 10:44, Andy Shevchenko wrote:
> +Cc: Surface community people.
> 
> On Sat, Sep 05, 2020 at 09:19:51AM +0100, Daniel Scally wrote:
>>
>> Following on from this thread:
>> https://www.spinics.net/lists/linux-driver-devel/msg135122.html -
>> apologies, can't see a way to reply to it directly.
> 
> Use lore [5] and its feature of downloading mailbox (or just seeing Message-Id
> which is enough for good MUA to attach reply properly to the thread).
> 
> [5]: https://lore.kernel.org/linux-media/12fbe3f5c6a16c5f3447adbc09fe27ceb2b16823.1589625807.git.mchehab+huawei@kernel.org/
> 

I also like to use the NNTP interface on lore:

nntp://nntp.lore.kernel.org

That lets you read/reply to many of the kernel lists without actually
having to subscribe. And of course gets the whole archive too.


>> Myself and others [1] have been trying to get cameras working on
>> Microsoft Surface and similar platforms, currently I'm working on
>> expanding Jordan's module connecting cameras to the cio2
>> infrastructure (which works - we can use it to take images), aiming to
>> discover connection information from SSDB in the DSDT, as well as
>> connect as many supported sensors as are found on the device. I'm just
>> struggling with a problem I've encountered using the swnode patch that
>> Heikki linked in that thread; the module's working ok when I only
>> attempt to connect a single one of my sensors (by preventing the
>> driver for the other sensor from loading, in which case this new
>> module ignores the sensor), but when I attempt to connect both cameras
>> at the same time I get a kernel oops as part of
>> software_node_get_next_child. The module is creating software_nodes
>> like this...
>>
>> /sys/kernel/software_node/INT343E/port0/endpoint0
>> /sys/kernel/software_node/INT343E/port1/endpoint0
>> /sys/kernel/software_node/OVTI2680/port0/endpoint0
>> /sys/kernel/software_node/OVTI5648/port0/endpoint0
>>
>> And that's the structure that I expect to see, but it seems like the
>> call to list_next_entry in that function is returning something that
>> isn't quite a valid swnode. Printing the address of c->fwnode after
>> that point returns "3", which isn't a valid address of course, and
>> that's causing the oops when it's either returned (in the version of
>> the function without the patches) or when the program flow tries to
>> call the "get" op against that fwnode (in the patched version). I've
>> been trying to track it down for a while now without success, so I
>> posted the problem on SO[2] and it was suggested that I mail these
>> addressees for advice - hope that that is ok.
>>
>>
>> My copy of Jordan's module is parked in my git repo [3] for now, and
>> requires a batch of patches from Jordan's repo [4] (one made by Heikki
>> to fill in the missing swnode graph pieces, and some further tweaks) -
>> I've been applying those against 5.8.0-rc7. Any other criticism more
>> than welcome - I'm new to both c and kernel programming so I'm happy
>> to take all the advice people have the time to give.
>>
>>
>> On a more general note; Kieran from the libcamera project suggested we
>> ought to be talking to you guys anyway to get some guidance on design,
>> and some more expert eye on the things we don't really understand. In
>> particular; we haven't been able to figure out how sensors that are
>> intended to work with the cio2 ipu3 stuff have their clock/regulators
>> supplied - in fact I can strip all the "usual" clock/regulator
>> functionality out of my camera's driver and it still functions fine,
>> which seems a bit weird. So far all we're doing as "power management"
>> of the camera's is turning on the GPIO pins that DSDT tables assign to
>> the tps68470 PMICs the cameras are theoretically hooked up to...but
>> given the drivers continue to work without using the PMICs regulator
>> and clk drivers (which we found in the intel-lts tree on Github),
>> we're a bit confused exactly how these are connected. Given the
>> potential for actual hardware damage if we mess something up there
>> it'd be great if anyone can shed some light on those elements.
> 
>> [1] https://github.com/linux-surface/linux-surface/issues/91
>> [2] https://stackoverflow.com/questions/63742967/what-is-causing-this-kernel-oops-when-parsing-firmware?
>> [3] https://github.com/djrscally/miix-510-cameras/blob/master/surface_camera/surface_camera.c
>> [4] https://github.com/jhand2/surface-camera/tree/master/patches
> 

-- 
Regards
--
Kieran