On 23/02/24 10:59, Andy Shevchenko wrote: > On Thu, Feb 22, 2024 at 11:53 PM Chris Packham > <Chris.Packham@xxxxxxxxxxxxxxxxxxx> wrote: >> On 23/02/24 10:34, andy.shevchenko@xxxxxxxxx wrote: >>> Sun, Feb 11, 2024 at 08:46:12PM +0000, Chris Packham kirjoitti: >>>> Hi Blinkenlight enthusiasts, >>>> >>>> I'm looking for something that I figured must exists but maybe it's so >>>> niche that no-one has bothered to upstream a driver for it. >>>> >>>> I have a requirement to support a 7-segment LED display[1] (one that can >>>> display a single digit from 0-9). Hardware wise it's just a bunch of >>>> individual GPIOs connected to each segment (plus an extra one for a >>>> dot). I can't see anything obvious in drivers/leds but maybe I'm looking >>>> in the wrong place. Or maybe it's the kind of thing on PC hardware that >>>> is just driven by the BIOS without the operating system knowing about it. >>>> >>>> Is there an existing in-kernel driver for such a thing? >>> No, and can't be. Here is just a mapping table and other drivers that use >>> 7-segment LED displays to be connected to. >>> >>> What you need is something else, i.e. special case of leds-gpio (which should >>> be somewhere else) that does something like this. To me it sounds like a >>> mixture between line-display.h (from auxdisplay) and gpio-aggregator. >>> >>> How many digits do you want to connect? How are they going to be connected >>> (static display, or dynamic when you need to refresh in certain periods of >>> time)? Depending on the answer it might take one or another approach. >> It sounds like a auxdisplay driver might be the way to go. My hardware >> happens to have a single 7seg block but there's no reason the driver >> needs to be restricted to that. At some point it obviously becomes >> better to fit something like the ht16k33 to offload the character >> display but for one or 2 digits a PCA953x plus the LED block would do >> just fine. > I have hc595 (SPI GPIO) connected to a single digit 7-segment LED. > Since it can be also serialized, line display APIs seem plausible to > fit. What we need is a proxy between the two. And I think > gpio-aggregator is the best for that. It needs an additional > compatible string and the registration for line display (overall > something like 50 LoCs). We can even call that hardware compatible as > line-display-gpio (or so). > > Cc: Geert and Krzysztof (for the comments on the idea above). Would the gpio-aggregator be necessary? I was thinking something like this in the devicetree \{ led-7seg { compatible = "kingbright,sa36"; seg-gpios = <&gpioN 0 GPIO_ACTIVE_HIGH>, <&gpioN 1 GPIO_ACTIVE_HIGH>, <&gpioN 2 GPIO_ACTIVE_HIGH>, <&gpioN 3 GPIO_ACTIVE_HIGH>, <&gpioN 4 GPIO_ACTIVE_HIGH>, <&gpioN 5 GPIO_ACTIVE_HIGH>, <&gpioN 6 GPIO_ACTIVE_HIGH>; }; }; > >> The information we want to display is mostly static (basically a numeric >> unit identifier) but there are cases where we may want to alternate >> between this and "F" to indicate some fault condition. >