[v2,00/18] auxdisplay: ht16k33: Add character display support

Hi all,

The Holtek HT16K33 LED controller is not only used for driving
dot-matrix displays, but also for driving segment displays.
The current auxdisplay driver is limited to dot-matrix displays, which
are exposed as a frame buffer device.

This patch series extends the driver to 4-digit 7-segment and quad
14-segment alphanumeric displays, allowing the user to display and
scroll text messages.

List of patches:
  - Patch 1 provides font data for displaying ASCII characters on
    14-segment displays,
  - Patch 2 updates the HT16K33 DT bindings for segment displays,
  - Patches 3-5 contain a bug fix and small improvements for the
    Imagination Technologies ASCII LCD Display driver,
  - Patch 6 extracts the character line display core support from the
    Imagination Technologies ASCII LCD Display driver, for reuse,
  - Patches 7-8 contain cleanups and improvements for the character line
    display core driver,
  - Patches 9-16 contain a bug fix, cleanups and improvements for the
    HT16K33 driver, to prepare for segment display support,
  - Patch 17 adds support for 7/14-segment displays to the HT16K33
    driver,
  - Patch 18 adds segment display LED support to the HT16K33 driver,
    to make use of hardware blinking, and to expose display color.

Changes compared to v1[1]:
  - Fix type of color to uint32,
  - "refresh-rate-hz" is still required for dot-matrix displays.
  - Move "select LINEDISP" for HT16K33 symbol to correct patch,
  - Add backwards compatibility "message" symlink to img-ascii-lcd,
  - Connect backlight to fbdev in ht16k33 dot-matrix mode,
  - Set "err = -EINVAL" in switch() case that cannot happen,
  - Use "auxdisplay" instead of DRIVER_NAME in LED name.

This series has been tested using an Adafruit 0.54" Quad Alphanumeric
Red FeatherWing Display, plugged into an OrangeCrab ECP5-based FPGA
board running linux-on-litex-vexriscv.
7-segment display support is based purely on schematics, and has not
been tested on actual hardware.  The changes to img-ascii-lcd.c are also
untested, due to lack of hardware.

Thanks for your comments!

[1] "[PATCH 00/17] auxdisplay: ht16k33: Add character display support"
    https://lore.kernel.org/r/20210322144848.1065067-1-geert@linux-m68k.org/

Geert Uytterhoeven (18):
  uapi: Add <linux/map_to_14segment.h>
  dt-bindings: auxdisplay: ht16k33: Document Adafruit segment displays
  auxdisplay: img-ascii-lcd: Fix lock-up when displaying empty string
  auxdisplay: img-ascii-lcd: Add helper variable dev
  auxdisplay: img-ascii-lcd: Convert device attribute to sysfs_emit()
  auxdisplay: Extract character line display core support
  auxdisplay: linedisp: Use kmemdup_nul() helper
  auxdisplay: linedisp: Add support for changing scroll rate
  auxdisplay: ht16k33: Connect backlight to fbdev
  auxdisplay: ht16k33: Use HT16K33_FB_SIZE in ht16k33_initialize()
  auxdisplay: ht16k33: Remove unneeded error check in keypad probe()
  auxdisplay: ht16k33: Convert to simple i2c probe function
  auxdisplay: ht16k33: Add helper variable dev
  auxdisplay: ht16k33: Move delayed work
  auxdisplay: ht16k33: Extract ht16k33_brightness_set()
  auxdisplay: ht16k33: Extract frame buffer probing
  auxdisplay: ht16k33: Add support for segment displays
  auxdisplay: ht16k33: Add segment display LED support

 .../bindings/auxdisplay/holtek,ht16k33.yaml   |  31 +-
 drivers/auxdisplay/Kconfig                    |   8 +
 drivers/auxdisplay/Makefile                   |   1 +
 drivers/auxdisplay/ht16k33.c                  | 458 ++++++++++++++----
 drivers/auxdisplay/img-ascii-lcd.c            | 206 ++------
 drivers/auxdisplay/line-display.c             | 261 ++++++++++
 drivers/auxdisplay/line-display.h             |  43 ++
 include/uapi/linux/map_to_14segment.h         | 239 +++++++++
 8 files changed, 989 insertions(+), 258 deletions(-)
 create mode 100644 drivers/auxdisplay/line-display.c
 create mode 100644 drivers/auxdisplay/line-display.h
 create mode 100644 include/uapi/linux/map_to_14segment.h

On Fri, 25 Jun 2021 22:39:16 +0200
Marek Behun <marek.behun@nic.cz> wrote:

> On Fri, 25 Jun 2021 14:59:02 +0200
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> 
> > Instantiate a single LED for a segment display.  This allows the user to
> > control display brightness and blinking through the LED class API and
> > triggers, and exposes the display color.
> > The LED will be named "auxdisplay:<color>:backlight".  
> 
> What if there are multiple "auxdisplay"s ?
> Doesn't this subsystem have IDs? So that you can use auxdisplayN for
> device name, for example?

Or if this driver creates a fbdev, maybe "fb<N>" for devicename?

Marek

Hi Marek,

On Fri, Jun 25, 2021 at 10:40 PM Marek Behun <marek.behun@nic.cz> wrote:
> On Fri, 25 Jun 2021 22:39:16 +0200

> Marek Behun <marek.behun@nic.cz> wrote:

> > On Fri, 25 Jun 2021 14:59:02 +0200

> > Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> > > Instantiate a single LED for a segment display.  This allows the user to

> > > control display brightness and blinking through the LED class API and

> > > triggers, and exposes the display color.

> > > The LED will be named "auxdisplay:<color>:backlight".

> >

> > What if there are multiple "auxdisplay"s ?

> > Doesn't this subsystem have IDs? So that you can use auxdisplayN for

> > device name, for example?

>

> Or if this driver creates a fbdev, maybe "fb<N>" for devicename?


This LED device is only registered when using the HT16K33 to drive
segment displays.
When driving a dot matrix display, the driver still use fbdev and
devm_backlight_device_register(), for backwards compatibility.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds