linux-kernel - Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel bindings

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Date:   Wed, 24 Aug 2016 13:56:39 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Vinay Simha BN <simhavcs@...il.com>
Cc:     Archit Taneja <archit.taneja@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel
 bindings

On Sun, Jul 31, 2016 at 08:45:21PM +0530, Vinay Simha BN wrote:
[...]
> diff --git a/Documentation/devicetree/bindings/display/panel/jdi,lt070me05000.txt b/Documentation/devicetree/bindings/display/panel/jdi,lt070me05000.txt
[...]
> +- reset-gpios: phandle of gpio for reset line
> +  This should be 8mA, gpio can be configured using mux, pinctrl, pinctrl-names
> +  XRES, Reset, Low active
> +- enable-gpios: phandle of gpio for enable line
> +  LED_EN, LED backlight enable, High active

This is a little confusing. Shouldn't we rather completely omit any
mention of the polarity of these and let the board design handle this?

If the reset is low active, then I'd expect that to be reflected in the
GPIO specifier of the reset-gpios property, like so:

	panel@0 {
		...
		reset-gpios = <&tlmm_pinmux 54 GPIO_ACTIVE_LOW>;
		...
	};

With that a driver can simply deal with a high active reset, which it
currently doesn't. The problem with the current description is that it
is unclear who's to deal with the polarity. In order for this to work
properly with the current driver you'll have to specify the GPIO as
GPIO_ACTIVE_HIGH, which is not what the binding says it should be.

Thierry

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