Re: [RFC 00/25] arm64: realtek: Add Xnano X5 and implement TM1628/FD628/AiP1618 LED controllers

From: Robin Murphy
Date: Thu Dec 12 2019 - 08:15:01 EST

Hi Andreas,

On 12/12/2019 3:39 am, Andreas FÃrber wrote:
Hello,

This patch series implements the LED controllers found in some RTD1295 based
TV set-top boxes.

Ever since I've had mainline Linux kernels booting on my Zidoo X9S TV box,
it's been bugging me that it kept displaying "boot" on its front display.
A hot lead was a TM1628 chip on the front display's daughterboard, which
English and Chinese datasheets were available for. The biggest hurdle
to overcome was whether and how this chip was connected to the SoC.
Confusingly the datasheet talks about "Serial Interface" and shows pins
DIO, SCLK and STB; whereas neither UART nor SPI DT nodes seemed to be in use
for this, no mention of such chipset in the binary vendor DT, and only one
seemingly unrelated exported GPIO. Sadly Zidoo have refused to share GPL
sourcecode with me, and the public GPL code drops from NAS and SBC vendors
didn't seem to include drivers for this chip. Last weekend, review of vendor
DT pinctrl nodes revealed a "spi@1" pinctrl node in use by the pinctrl node
itself, despite there being only one GSPI block on the SoC. debugfs under
Android revealed GPIO pins named "fp_stb", "fp_data" and "fp_clk" (on X5:
3x "vfdtest", unhelpfully). So I hereby present my first 3-wire SPI slave,
using standard spi-gpio driver.

This required to extend the spi-gpio driver with Little Endian support.

TM1628 and related chipsets have an internal Display RAM, from which they
control a two-dimensional array of LED components, often used for
seven-segment displays, i.e. clock display, but also for indicators.
Individual LEDs can be turned on/off, but brightness is applied globally.
Some chipsets also support polling a two-dimensional key pad.

This initial RFC implements a SPI slave driver within Linux leds subsystem
and lets DT expose individual LED components as two-state LEDs, allowing
to assign standard Linux LED triggers and to control them via sysfs.

It goes on to add a "text" attribute to the driver that enables DT-configured
seven-segment displays; I was expecting to find precedence in auxdisplay
subsystem but came up empty. So my driver currently integrates its own
generic (but incomplete) character-to-8-segments mapping, as well as in a
second step a combined-characters-to-8-segments mapping, which then gets
mapped to the chipset's available output lines. Doing this as sysfs device
attribute had the advantage of being able to test it quickly; it also leaves
timezone management to userspace and lets it choose between wall clock and
playback time as needed. LED triggers appeared to be per-LED; otherwise an
RTC-implemented interrupt based LED trigger would've been nice for RTD1195+,
since my pending irqchip driver exposes interrupts down to half-second that
would seem ideal for accurately driving such a display, with blinking colon.

Finally, it sketches how keypad handling could be integrated into the leds
driver, but I am lacking a test case for that functionality.
Distinguishing LEDs and key inputs in DT may get difficult...

For brightness control I am still investigating the backlight API and
defaulting to the chipset's default (lowest) brightness.

Prepended is a new DT for Xnano X5 OTT TV Box, featuring an FD628 display.

Displays connected to these controllers didn't have any model or vendor
usually, and for the lengthy numbers from my X9S, Google found no hits.
Therefore I've been unable to come up with compatible strings for those
displays and need to configure it per .dts, even though some may be using
the same, e.g., "88:88" type display model.
Whereas the same display might be connected to different LED controllers,
thus is orthogonal to the controller's compatible string.

Another aspect here is that the leds binding expects to have child nodes
per LED directly on the LED controller node. So I've gone to lengths to
shoehorn my display child node into that scheme via wildcard reg property.

The alternative would be to define some special child node, as done for the
SPI controller's "slave" node, to use as display. But in theory there might
be multiple displays connected to one controller (which is neglected here).
And in theory the same display might be wired up differently, so at most
the display model could tell us about layout and availability of LEDs, but
we'd still need a mapping from the LED controller's to the display's pins.
So far neither of the two displays tested actually use the segment lines
for the segments, but rather switch segment and grid lines.

So in theory we might consider the display as LED controller and implement
binding/driver on that level (moving it to DT root node like gpio-leds),
if we can hook it up to the actual LED controller in this case on SPI bus?
Assuming we can actually identify the display with some compatible string,
that is.
However, update efficiency has been a concern, with clock display in mind.
Thus, forcing two SPI commands (three SPI transfers) per LED segment, as the
the current LED API would entail, should better be avoided. This led to the
current design of having everything in tm1628 driver, so that we can easily
determine the scope of an update operation there (one per LED; all for text,
to be optimized through bit field of dirtied bytes).

Locking is completely missing still. We'll need at least a mutex to avoid,
e.g., a heartbeat LED trigger and a text update conflicting on SPI bus or
"hazards" becoming visible on the display during conflicting byte updates.

Module remove support is missing, too.

We may also need to revisit my error checking and either inline functions
or drop checks on the LED bit level, if it becomes a performance bottleneck.

On the cosmetic side, some lines are still beyond 80 characters.

Some more notes:
* Public TM1628 V1.1 datasheet is in Chinese only and differs from the
unversioned English version found elsewhere on datasheet sites by
documenting more display modes, included here (guessed from Arabic numbers).
* Public FD628 datasheet is Chinese only (guesses based on Arabic numbers).
FD623 appears to have more output lines, which would fit current data types.
* AiP1618 links were all broken (404); try Google "site:szfdwdz.com" search
to actually find the documents available on their site.
* Princeton PT6964 is another related LED controller with public datasheet
that I did not encounter in my TV boxes yet, thus not included here.
Datasheets are linked only for PT6959 and PT6967, but PT6964 V1.3 and V1.4
are available elsewhere. PT6967 has more output lines, which my current
data types could barely hold. Maybe bump them all to u32 type right away?
* TM1628 is also found on MeLE V9 TV box, to be tested.
* FD628 is also found on Amlogic S905X2 based Vontar X96 Max TV box,
to be tested (once UART is soldered).
* AiP1618 was found on Ava and Lake I TV boxes, to be tested.
* It remained unclear to me which of these many similar chipsets was first.
My driver name is therefore based on the chip I encountered first.

It's pretty cool to see this! My Rockchip box has an AiP1618-driven display that I've also spent a bit of time hacking around with - I did get some way into writing an LED driver, but ultimately gave up and wrote a simple thing to bit-bang the GPIO chardev from userspace (and since there are enough clocks in my house, I now have a cpufreq display!)

In case it helps, in my research I found that ARTSCHIP are another vendor of these things with accessible datasheets[1], and as far as I could tell the command set appears to derive from (or is at least common to) some old Holtek VFD controllers.

If I can figure out the DT parts (which was one of the areas that stalled my attempt) I'll try to have a play with this series over the holidays. One thought to ponder is that I have an "88:88" display where the entire middle grid is reserved for the colon (which is wired to just one segment) - I'm not sure how that could be sanely described :/

Robin.

[1] http://www.artschip.com/products.asp?lx=small&anid=779&ParentName=Signal%20management%20_I_O%20Extender

This series is based on my not-yet-posted RTD1295 pinctrl and GPIO drivers.

Latest experimental patches at:
https://github.com/afaerber/linux/commits/rtd1295-next

Have a lot of fun!

Cheers,
Andreas

Cc: linux-leds@xxxxxxxxxxxxxxx
Cc: Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: Dan Murphy <dmurphy@xxxxxx>

Cc: linux-rtc@xxxxxxxxxxxxxxx
Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>

Cc: devicetree@xxxxxxxxxxxxxxx
Cc: Rob Herring <robh+dt@xxxxxxxxxx>

Cc: linux-spi@xxxxxxxxxxxxxxx
Cc: Mark Brown <broonie@xxxxxxxxxx>

Cc: linux-amlogic@xxxxxxxxxxxxxxxxxxx

Cc: Roc He <hepeng@xxxxxxxx>
# No email for Xnano

Cc: zypeng@xxxxxxxxxxxx
Cc: sales@xxxxxxxxxx
# No email for szfdwdz.com
Cc: csd@xxxxxxxxxxxxxxxx

Andreas FÃrber (25):
dt-bindings: vendor-prefixes: Add Xnano
dt-bindings: arm: realtek: Add Xnano X5
arm64: dts: realtek: rtd1295: Add Xnano X5
spi: gpio: Implement LSB First bitbang support
dt-bindings: vendor-prefixes: Add Titan Micro Electronics
dt-bindings: leds: Add Titan Micro Electronics TM1628
leds: Add Titan Micro Electronics TM1628
arm64: dts: realtek: rtd129x-zidoo-x9s: Add TM1628 LED controller
arm64: dts: realtek: rtd1295-zidoo-x9s: Add regular LEDs to TM1628
dt-bindings: vendor-prefixes: Add Fuda Hisi Microelectronics
dt-bindings: leds: tm1628: Add Fuda Hisi Microelectronics FD628
leds: tm1628: Add Fuda Hisi Microelectronics FD628
arm64: dts: realtek: rtd1295-xnano-x5: Add FD628 LED controller
arm64: dts: realtek: rtd1295-xnano-x5: Add regular LEDs to FD628
dt-bindings: vendor-prefixes: Add Fude Microelectronics
dt-bindings: leds: tm1628: Add Fude Microelectronics AiP1618
leds: tm1628: Prepare Fude Microelectronics AiP1618
dt-bindings: leds: tm1628: Define display child nodes
leds: tm1628: Add 7-segment display support
arm64: dts: realtek: rtd1295-zidoo-x9s: Add display to TM1628
arm64: dts: realtek: rtd1295-xnano-x5: Add display to FD628
leds: tm1826: Add combined glyph support
WIP: leds: tm1628: Prepare TM1628 keys
WIP: leds: tm1628: Prepare FD628 keys
WIP: leds: tm1628: Prepare AiP1618 keys

Documentation/devicetree/bindings/arm/realtek.yaml | 1 +
.../devicetree/bindings/leds/titanmec,tm1628.yaml | 134 ++++
.../devicetree/bindings/vendor-prefixes.yaml | 8 +
arch/arm64/boot/dts/realtek/Makefile | 1 +
arch/arm64/boot/dts/realtek/rtd1295-xnano-x5.dts | 108 +++
arch/arm64/boot/dts/realtek/rtd1295-zidoo-x9s.dts | 36 +-
drivers/leds/Kconfig | 12 +
drivers/leds/Makefile | 1 +
drivers/leds/leds-tm1628.c | 727 +++++++++++++++++++++
drivers/spi/spi-bitbang-txrx.h | 68 +-
drivers/spi/spi-gpio.c | 42 +-
11 files changed, 1126 insertions(+), 12 deletions(-)
create mode 100644 Documentation/devicetree/bindings/leds/titanmec,tm1628.yaml
create mode 100644 arch/arm64/boot/dts/realtek/rtd1295-xnano-x5.dts
create mode 100644 drivers/leds/leds-tm1628.c