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

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  Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel  bindings Thierry Reding <thierry.reding@gmail.com> - 2016-08-24 14:00 +0200
    Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel bindings Vinay Simha <simhavcs@gmail.com> - 2016-08-24 14:30 +0200
      Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel  bindings Thierry Reding <thierry.reding@gmail.com> - 2016-08-24 14:40 +0200

#1469367 — Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel bindings

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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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#1469383 — Re: [RESEND] [PATCH v2 2/4] dt-bindings: Add jdi lt070me05000 panel bindings

if we do not set the polarity to 8mA, panel will have gibberish display.
(information to set 8mA is available only in
nexus7-msm-flo-3.4-lollipop-release_dsi kernel nx7 release)

i will add this
reset-gpios = <&tlmm_pinmux 54 GPIO_ACTIVE_LOW>;

On Wed, Aug 24, 2016 at 5:26 PM, Thierry Reding
<thierry.reding@gmail.com> wrote:
> 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



-- 
regards,
vinaysimha

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#1469384

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On Wed, Aug 24, 2016 at 05:53:00PM +0530, Vinay Simha wrote:
> if we do not set the polarity to 8mA, panel will have gibberish display.
> (information to set 8mA is available only in
> nexus7-msm-flo-3.4-lollipop-release_dsi kernel nx7 release)
> 
> i will add this
> reset-gpios = <&tlmm_pinmux 54 GPIO_ACTIVE_LOW>;

I don't think that will work with the current driver, because the GPIO
subsystem will automatically invert the value for you. Currently the
panel driver sets the GPIO value to 0 to assert the reset. With the
GPIO_ACTIVE_LOW flag you'd end up setting the actual level of the GPIO
to high, which is going to deassert. So I think if you make the above
change (which I think is the right thing to do), you'll also have to
update the driver to use high-active logic.

Thierry

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