linux-kernel - Re: [PATCH linux v1 0/4] Seven segment display support

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Date:   Wed, 14 Dec 2016 04:56:41 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:     Jaghathiswari Rankappagounder Natarajan <jaghu@...gle.com>,
        openbmc@...ts.ozlabs.org, robh+dt@...nel.org, mark.rutland@....com,
        linux@...linux.org.uk, arnd@...db.de, joel@....id.au,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH linux v1 0/4] Seven segment display support

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...

thanks,

greg k-h