LinuxLists.cc - [PATCH v3 0/5] Support ROHM BU27008 RGB sensor

2023-04-26 08:08:11

Subject: [PATCH v3 0/5] Support ROHM BU27008 RGB sensor

Add support for ROHM BU27008 RGB sensor.

The ROHM BU27008 is a sensor with 5 photodiodes (red, green, blue, clear
and IR) with four configurable channels. Red and green being always
available and two out of the rest three (blue, clear, IR) can be
selected to be simultaneously measured. Typical application is adjusting
LCD backlight of TVs, mobile phones and tablet PCs.

This series supports reading the RGBC and IR channels using IIO
framework. However, only two of the BC+IR can be enabled at the same
time. Series adds also support for scale and integration time
configuration, where scale consists of impact of both the integration
time and hardware gain. The gain and time support is backed by the newly
introduced IIO GTS helper. This series depends on GTS helper patches
added in BU27034 support series which is already merged in iio/togreg
which this series is based on.

The hardware allows configuring gain setting by writing a 5-bit gain
selector value to a register. Part of the gain setting is common for all
channels (RGBC + IR) but part of the selector value can be set
separately for RGBC and IR:

MODE_CONTROL2 REG:
bit 7 6 5 4 3 2 1 0
-----------------------------------------------------------------
| RGB selector |
+---------------------------------------+
-----------------------------------------------------------------
| high bits IR | | low bits IR selector |
+---------------+ +-----------------------+

In theory it would be possible to set certain separate gain values for
RGBC and IR channels, but this gets pretty confusing because there are a
few 'unsupported' selector values. If only RGBC or IR was set, some
extra handling should be done to prevent the other channel from getting
unsupported value due to change in high-bits. Furthermore, allowing the
channels to be set different gain values (in some cases when gains are
such the HW supports it) would make the cases where also integration
time is changed to achieve correct scale ... interesting. It might also
be confusing for user to try predicting when setting different scales
succeeds and when it does not. Furthermore, if for example the scale
setting for RGBC caused IR selector to be invalid - it could also cause
the IR scale to "jump" very far from previous value.

To make the code simpler and more predictable for users, the current
logic is as follows:

1. Prevent setting IR scale. (My assumption is IR is less used than
RGBC)
2. When RGBC scale is set, set also the IR-selector to the same value.
This prevents unsupported selector values and makes the IR scale changes
predictable.

The 2) could mean we effectively have the same scale for all channels.
Unfortunately, the HW design is slightly peculiar and selector 0 means
gain 1X on RGBC but gain 2X on IR. Rest of the selectors equal same gain
values on RGBC and IR. The result is that while changin selector from 0
=> 1 causes RGBC gain to go from 1X => 4X, it causes IR gain to go from
2X => 4X.

So, the driver provides separate scale entries for all channels (also
RGB and C will have separate gain entries because these channels are of
same type as IR channel). This makes it possible for user applications
to go read the scales for all channels after setting scale for one (in
order to detect the IR scale difference).

Having the separate IR scale entry which applications can read to detect
"arbitrary scale changes" makes it possible for applications to be
written so they can cope if we need to implement the 'allow setting some
different gains for IR and RGBC' - later.

Finally, the scales_available is also provided for all other channels
except the IR channel, which does not allow the scale to be changed.

The sensor provides a data-ready IRQ and the driver implements a
triggered buffer mode using this IRQ as a trigger.

Finally, the series introduces generic iio_validate_own_trigger() helper
which can be used as a validate_trigger callback for drivers which
require the trigger and iio-device to be parented by same device. The
KX022A driver is converted to use this new callback instead of rolling
it's own function. The new helper and KX022A can be merged in as
independent changes if need be.

Revision history
v2 => v3:
dt-bindings:
- No changes
iio_validate_own_trigger:
- subject fix
bu27008:
- Mostly styling based on comments from Andy and Andi

More accurate changelog in individual patches

v1 => v2:
dt-bindings:
- Fix issues pointed by Krzysztof.
bu27008 driver:
- Fix issues pointed by Jonathan
Add new helper for validating own trigger

More accurate changelog in individual patches

---

Matti Vaittinen (5):
dt-bindings: iio: light: ROHM BU27008
iio: trigger: Add simple trigger_validation helper
iio: kx022a: Use new iio_validate_own_trigger()
iio: light: ROHM BU27008 color sensor
MAINTAINERS: Add ROHM BU27008

.../bindings/iio/light/rohm,bu27008.yaml | 49 +
MAINTAINERS | 3 +-
drivers/iio/accel/kionix-kx022a.c | 13 +-
drivers/iio/industrialio-trigger.c | 22 +-
drivers/iio/light/Kconfig | 14 +
drivers/iio/light/Makefile | 1 +
drivers/iio/light/rohm-bu27008.c | 963 ++++++++++++++++++
include/linux/iio/trigger.h | 1 +
8 files changed, 1052 insertions(+), 14 deletions(-)
create mode 100644 Documentation/devicetree/bindings/iio/light/rohm,bu27008.yaml
create mode 100644 drivers/iio/light/rohm-bu27008.c

base-commit: 52cc189b4fc6af6accc45fe7b7053d76d8724059
--
2.40.0

--
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =]

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2023-04-26 08:08:25

by Matti Vaittinen

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On Sun, 7 May 2023 19:13:38 +0300
Matti Vaittinen <[email protected]> wrote:

> On 5/7/23 17:22, Jonathan Cameron wrote:
>
> >>> If there is nothing to do in the actual interrupt as it's a data ready
> >>> only signal, then you should just call iio_trigger_poll() in the top half and
> >>> use devm_request_irq() only as there is no thread in this interrupt (though
> >>> there is one for the interrupt below the software interrupt chip).
> >>
> >> I haven't tested this yet so please ignore me if I am writing nonsense -
> >> but... The BU27008 will keep the IRQ line asserted until a register is
> >> read. We can't read the register form HW-IRQ so we need to keep the IRQ
> >> disabled until the threaded trigger handler is ran. With the setup we
> >> have here, the IRQF_ONESHOT, took care of this. I assume that changing
> >> to call the iio_poll_trigger() from top-half means I need to explicitly
> >> disable the IRQ and re-enable it at the end of the trigger thread after
> >> reading the register which debounces the IRQ line?
> >
> > Hmm. I'm trying to remember how this works (wrote this a very long time ago).
> > I'm fairly sure it's not an issue because we use IRQF_ONESHOT down one level
> > so exercise the same prevention of the threads triggering multiple times etc >
> https://elixir.bootlin.com/linux/latest/source/drivers/iio/buffer/industrialio-triggered-buffer.c#L57
> >
> > It doesn't matter if the device interrupt fires again as it will still be masked
> > at our software irqchip level and will then get queued up and the thread will
> > run again.
>
> After reading this I am not at all sure I am using the trigger
> correctly. I see the iio_trigger_attach_poll_func() registering threaded
> handler with the IRQF_ONESHOT which is stored in the
> iio_alloc_pollfunc() as you pointed above.
>
> The iio_trigger_attach_poll_func() is called from sysfs callback when
> trigger is enabled. So, if this is supposed to be the device IRQ, then I
> am not at all sure the driver should be requesting the IRQ at the
> probe(). If it is not the device's IRQ, then I guess the IRQF_ONESHOT
> passed in here won't help. I need to try seeing some examples how other
> drivers are using the triggers. Getting back to this tomorrow...

I think you are confusing two different irqs here / I managed to confuse
you even more.

The one in iio_trigger_attach_pollfunc() is a child of the trigger - it's
called when the trigger 'fires' along with any other children attached
(if multiple IIO devices have current_trigger set tot his one).
The one you are registering for is the parent of the trigger and calls
iio_poll_trigger() in it's handler which in turn will result in interrupts
for any children of the trigger (that is the pollfunc's which are
interrupt handlers underneath).

Not sure this horrible diagram will help

Data Ready Interrupt
|
iio_trigger_poll() after checking it's right int etc. Easy here.
|
________|__________________________________________________________________
| | | |
Pollfunc 1 Int Pollfunc 2 Int
| |
Top half of PF 1 Top half of PF2 return IRQ_THREAD etc
| |
.....................................
| |
Thread PF 1 Thread PF 2
| |
iio_push_to_buffers..() iio_push_to_bufffers..()
For trigger consumer For trigger consumer
device 1 device 2.

So in the pollfunc interrupts have IRQF_ONESHOT set so the masking happens
in the internal irq_chip that IIO uses to handle this demux of the
trigger signal to multiple different sensor drivers to make them grab
data to push into buffers. This whole thing is built to enable
sync capture of multiple signals where possible (hardware restrictions
mean this only works for some combinations).
Years ago, we had our own registration scheme that didn't use interrupts
internally and it was pointed out (Arnd Bergmann I think...) that we
were just replicating what goes on in an interrupt chip so should use
that instead.

Jonathan

>
> Yours,
> -- Matti.
>