From: rajeevny@codeaurora.org
To: Doug Anderson <dianders@chromium.org>, Rob Herring <robh@kernel.org>
Cc: dri-devel <dri-devel@lists.freedesktop.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Rob Clark <robdclark@gmail.com>,
mkrishn@codeaurora.org, Kalyan Thota <kalyan_t@codeaurora.org>,
"Kristian H. Kristensen" <hoegsberg@chromium.org>,
Abhinav Kumar <abhinavk@codeaurora.org>,
Sean Paul <seanpaul@chromium.org>,
Jani Nikula <jani.nikula@linux.intel.com>,
Lyude Paul <lyude@redhat.com>,
"Lankhorst, Maarten" <maarten.lankhorst@intel.com>
Subject: Re: [v3 1/2] dt-bindings: backlight: add DisplayPort aux backlight
Date: Fri, 30 Apr 2021 20:40:15 +0530 [thread overview]
Message-ID: <78c4bd291bd4a17ae2a1d02d0217de43@codeaurora.org> (raw)
In-Reply-To: <CAD=FV=V-kdySH5Pp-Fb-PRYk60Ha_UOTXJHcvMp+uV3P1oo7Uw@mail.gmail.com>
On 30-04-2021 02:33, Doug Anderson wrote:
> Hi,
>
> On Thu, Apr 29, 2021 at 11:04 AM Rob Herring <robh@kernel.org> wrote:
>>
>> On Mon, Apr 26, 2021 at 11:29:15AM +0530, Rajeev Nandan wrote:
>> > Add bindings for DisplayPort aux backlight driver.
>> >
>> > Changes in v2:
>> > - New
>> >
>> > Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
>> > ---
>> > .../bindings/leds/backlight/dp-aux-backlight.yaml | 49 ++++++++++++++++++++++
>> > 1 file changed, 49 insertions(+)
>> > create mode 100644 Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml
>> >
>> > diff --git a/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml
>> > new file mode 100644
>> > index 00000000..0fa8bf0
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml
>> > @@ -0,0 +1,49 @@
>> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> > +%YAML 1.2
>> > +---
>> > +$id: http://devicetree.org/schemas/leds/backlight/dp-aux-backlight.yaml#
>> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> > +
>> > +title: DisplayPort aux backlight driver bindings
>> > +
>> > +maintainers:
>> > + - Rajeev Nandan <rajeevny@codeaurora.org>
>> > +
>> > +description:
>> > + Backlight driver to control the brightness over DisplayPort aux channel.
>> > +
>> > +allOf:
>> > + - $ref: common.yaml#
>> > +
>> > +properties:
>> > + compatible:
>> > + const: dp-aux-backlight
>> > +
>> > + ddc-i2c-bus:
>> > + $ref: /schemas/types.yaml#/definitions/phandle
>> > + description:
>> > + A phandle to the system I2C controller connected to the DDC bus used
>> > + for the DisplayPort AUX channel.
>> > +
>> > + enable-gpios:
>> > + maxItems: 1
>> > + description: GPIO specifier for backlight enable pin.
>> > +
>> > + max-brightness: true
>> > +
>> > +required:
>> > + - compatible
>> > + - ddc-i2c-bus
>> > +
>> > +additionalProperties: false
>> > +
>> > +examples:
>> > + - |
>> > + backlight {
>> > + compatible = "dp-aux-backlight";
>> > + ddc-i2c-bus = <&sn65dsi86_bridge>;
>> > + enable-gpios = <&tlmm 12 GPIO_ACTIVE_HIGH>;
>>
>> So the DDC bus is connected to a backlight and also a panel? This
>> binding is not reflecting the h/w, but rather what you want for some
>> driver.
>>
>> There's only one thing here and that's an eDP panel which supports
>> backlight control via DP aux channel. You can figure all that out from
>> the panel's compatible and/or reading the EDID.
>>
>> You might also be interested in this thread:
>>
>> https://lore.kernel.org/lkml/YIKsDtjcIHGNvW0u@orome.fritz.box/
>
> I think Rajeev needs to rework everything anyway as per:
>
> https://lore.kernel.org/r/87zgxl5qar.fsf@intel.com
>
> ...but you're right that it makes sense not to model the backlight as
> a separate node in the device tree. The panel driver can handle
> setting up the backlight.
>
> -Doug
It was not a good idea to create a separate backlight driver and use
ddc-i2c-bus to get access to DP aux. I am working to move the code
to the panel driver and to utilize the new DRM helper functions
(drm_edp_backlight_*) Lyude has added [1].
To use these helper functions, the panel driver should have access to
the
"struct drm_dp_aux *". The simple-panel has a "ddc-i2c-bus" property
to give the panel access to the DDC bus and is currently being used to
get the EDID from the panel. Can I use the same ddc bus i2c_adapter to
get
the "struct drm_dp_aux *"?
As per the suggestion [2], I get the "struct drm_dp_aux *" from the
i2c_adapter of ddc bus (maybe I didn't understand the suggestion
correctly),
and, it turned out, the way I have implemented is not the right way [3].
So, I am afraid to use the same method in the panel driver.
[1] https://lore.kernel.org/dri-devel/871rb5bcf9.fsf@intel.com/
[2] https://www.spinics.net/lists/dri-devel/msg295429.html
[3]
https://lore.kernel.org/dri-devel/20210426111116.4lc3ekxjugjr3oho@maple.lan/
Thanks,
Rajeev
next prev parent reply other threads:[~2021-04-30 15:10 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-26 5:59 [v3 0/2] drm: Add support for backlight control of eDP panel on ti-sn65dsi86 bridge Rajeev Nandan
2021-04-26 5:59 ` [v3 1/2] dt-bindings: backlight: add DisplayPort aux backlight Rajeev Nandan
2021-04-26 21:04 ` Rob Herring
2021-04-29 18:04 ` Rob Herring
2021-04-29 21:03 ` Doug Anderson
2021-04-30 15:10 ` rajeevny [this message]
2021-04-30 21:38 ` Doug Anderson
2021-05-11 18:11 ` rajeevny
2021-05-11 22:33 ` Laurent Pinchart
2021-05-11 23:17 ` Doug Anderson
2021-05-17 20:21 ` Doug Anderson
2021-05-25 8:03 ` rajeevny
2021-04-26 5:59 ` [v3 2/2] backlight: Add DisplayPort aux backlight driver Rajeev Nandan
2021-04-26 9:49 ` Jani Nikula
2021-04-26 14:57 ` rajeevny
2021-04-30 18:48 ` Lyude Paul
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