On Wednesday, December 14, 2016 2:12:41 PM CET Neil Armstrong wrote: > On 12/14/2016 01:56 PM, Greg KH wrote: > > On Wed, Dec 14, 2016 at 01:45:30PM +0100, Thomas Petazzoni wrote: > >> Hello, > >> > >> On Tue, 13 Dec 2016 23:55:00 -0800, Jaghathiswari Rankappagounder > >> Natarajan wrote: > >> > >>> Documentation for the binding which provides an interface for adding clock, > >>> data and clear signal GPIO lines to control seven segment display. > >>> > >>> The platform device driver provides an API for displaying on two 7-segment > >>> displays, and implements the required bit-banging. The hardware assumed is > >>> 74HC164 wired to two 7-segment displays. > >>> > >>> The character device driver implements the user-space API for letting a user > >>> write to two 7-segment displays including any conversion methods necessary > >>> to map the user input to two 7-segment displays. > >>> > >>> Adding clock, data and clear signal GPIO lines in the devicetree to control > >>> seven segment display on zaius platform. > >>> > >>> The platform driver matches on the device tree node; the platform driver also > >>> initializes the character device. > >>> > >>> Tested that the seven segment display works properly by writing to the > >>> character device file on a EVB AST2500 board which also has 74HC164 wired > >>> to two 7-segment displays. > >> > >> FWIW, I proposed a driver for seven segment displays back in 2013: > >> > >> http://lists.infradead.org/pipermail/linux-arm-kernel/2013-January/139986.html > >> > >> And the feedback from Greg KH was: we don't need a driver for that, do > >> it from userspace. See: > >> > >> http://lists.infradead.org/pipermail/linux-arm-kernel/2013-January/139992.html > >> > >> So: good luck > > > > Did anyone ever write a library for this type of thing? > > > > Again, I don't want to see one-off drivers for random devices like this > > that should be able to all be controlled from userspace in a common > > manner. Much like we did for fingerprint readers a long long time > > ago... > > > Actually, it's more than a random interface, a lot of SoCs and boards actually have such displays > and it's a pity to use UIO, sysfs gpio bitbanging and all sort of ugly stuff to only print a few > characters a simple and clean driver could achieve. > Some very well known SoCs even have integrated registers to lower the BOM and bypass the need for > a 74HC164 like component and avoid gpio bit banging. > > My personal concern is that you could also need to drive more segments, thus 7-segments > is too restrictive. > > But this driver is well structured, the gpio-bitbanging sub-driver is welcome. Maybe we can find a way to fit this into the existing drivers/leds/ subsystem? That already supports blinking, brightness and colour attributes of LEDs, so could this be extended to support (one of) digit, number, character or string with a common sysfs attribute and a way to hook up a led driver to that? Arnd -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
