Re: [PATCH 1/3] platform/x86: int3472: Add TPS68470 board data for Dell 7320 Detachable

[Sahan Nissanka <adee.sahan@gmail.com>]

Please do not apply this patch. The GPIO mapping in it is wrong, and I would
rather say so than have it land.

Charles Drolet, who has the same machine, reported against my out-of-tree
repository [1] that the front sensor probes with no pin assignment at all.
That is why a wrong mapping is invisible here: the real reset line sits
released by default, so the camera comes up either way. Two specifics.

There is no powerdown pin. This part needs no hardware to confirm - ov5675.c
requests only "reset", via devm_gpiod_get_optional(dev, "reset", ...), and no
"powerdown" con_id exists anywhere in that driver. So

	GPIO_LOOKUP("tps68470-gpio", 4, "powerdown", GPIO_ACTIVE_LOW),

is never looked up. It is dead code, and my belief that the pin was needed was
unfounded.

The reset is on tps68470-gpio 5, not 3. Charles held the line with gpioset
against a build with no pin assignment, so nothing else had claimed it, and
reloaded the module: held low the sensor fails to identify with -EIO, released
it identifies correctly. That is consistent with an active-low reset on line
5. I have not reproduced this myself yet.

I should also correct how I arrived at 3 and 4. I took them from the Dell 7212
and 5290 board data as prior art, and treated "the camera works" as
confirmation. It is not. It confirms the sensor runs; it says nothing about
whether the mapping describes this board.

The rail mapping may need revisiting too. Charles has avdd on AUX1 at 2.8 V
where this patch has it on VSIO at 1.8 V, and the part wants roughly 2.8 V
analogue. Both configurations work, which suggests these rails may serve as
enables for regulators further down the line rather than as the supplies
themselves. I would rather resolve that than guess again.

The machine this work was done on was a loan and has gone back. A second 7320
Detachable arrives in the next few days, and I will verify the mapping on it
before sending a v2 - including checking whether the board data generalises
across units or merely described the one I had.

Patches 2/3 and 3/3 are not affected by any of this. Charles independently
arrived at the same ipu-bridge entry and the same ACPI id addition.

My thanks to Charles for finding this and for testing it properly.

[1] https://github.com/githomeserver/latitude-7320-camera/issues/1

--
Sahan Nissanka