From: Tomi Valkeinen <tomi.valkeinen@ti.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thierry Reding <thierry.reding@avionic-design.de>,
Tomi Valkeinen <tomba@iki.fi>, Alex Courbot <acourbot@nvidia.com>,
Grant Likely <grant.likely@secretlab.ca>,
Anton Vorontsov <cbouatmailru@gmail.com>,
Stephen Warren <swarren@nvidia.com>,
Mark Zhang <markz@nvidia.com>,
Rob Herring <rob.herring@calxeda.com>,
Mark Brown <broonie@opensource.wolfsonmicro.com>,
David Woodhouse <dwmw2@infradead.org>,
Arnd Bergmann <arnd@arndb.de>,
"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
"devicetree-discuss@lists.ozlabs.org"
<devicetree-discuss@lists.ozlabs.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
Alexandre Courbot <gnurou@gmail.com>
Subject: Re: [PATCHv9 1/3] Runtime Interpreted Power Sequences
Date: Tue, 27 Nov 2012 17:19:05 +0200 [thread overview]
Message-ID: <50B4D9E9.8070607@ti.com> (raw)
In-Reply-To: <6982060.HfOokt4dIn@avalon>
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On 2012-11-27 17:08, Laurent Pinchart wrote:
> Hi Tomi,
>
> On Wednesday 21 November 2012 14:04:17 Tomi Valkeinen wrote:
>> On 2012-11-21 13:40, Thierry Reding wrote:
>
> [snip]
>
>>> One thing that's not very clear is how the backlight subsystem should be
>>> wired up with the display framework. I have a patch on top of the Tegra
>>> DRM driver which adds some ad-hoc display support using this power
>>> sequences series and the pwm-backlight.
>>
>> I think that's a separate issue: how to associate the lcd device and
>> backlight device together. I don't have a clear answer to this.
>>
>> There are many ways the backlight may be handled. In some cases the
>> panel and the backlight are truly independent, and you can use the other
>> without using the other (not very practical, though =).
>
> From a control point of view that's always the case for DPI panels (as those
> panels have no control bus, the backlight control bus is by definition
> separate) and is the case for the two DBI panels I've seen (but I won't claim
> that's a significative number of panels).
They may have a control bus, I2C, SPI, etc. In some cases that can be
used to control the backlight. But yes, it's separate from the video bus.
>> But then with some LCDs the backlight may be controlled by sending commands
>> to the panel, and in this case the two may be quite linked. Changing the
>> backlight requires the panel driver to be up and running, and sometimes the
>> sending the backlight commands may need to be (say, DSI display, with
>> backlight commands going over the DSI bus).
>
> When you write "sending commands to the panel", do you mean on the same
> control bus that the panel use ? Or would that also include for instance an
> I2C backlight controller integrated inside a DSI panel module ? In the later
I mean the same control bus that is used to control the panel, be it
shared with video bus like DSI, or separate like I2C.
> case there might still be dependencies between the panel controller and the
> backlight controller (let's say for instance that the panel controller has a
> DSI-controller GPIO wired to the backlight controller reset signal), but in
> practice I don't know if that's ever the case.
>
>> So my feeling is that the panel driver should know about the related
>> backlight device. In the first case the panel driver would just call
>> enable/disable in the backlight device when the panel is turned on.
>
> That makes sense. Unless I'm mistaken a backlight is always associated with a
> panel (it would be called a light if there was no panel in front of it). We
> can thus expose backlight operations in the panel CDF (in-kernel) API. The
> panel driver would need a way to retrieve a pointer to the associated
> backlight device.
I agree.
>> In the second case of the DSI panel... I'm not sure. I've implemented it
>> so that the panel driver creates the backlight device, and implements
>> the backlight callbacks. It then sends the DSI commands from those
>> callbacks.
>
> If we decide to make the panel expose backlight operations we could get rid of
> the backlight device in this case.
Do you mean there would be a real backlight device only when there's a
totally independent backlight for the panel?
Tomi
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next prev parent reply other threads:[~2012-11-27 15:19 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-17 10:55 [PATCHv9 0/3] Runtime Interpreted Power Sequences Alexandre Courbot
2012-11-17 10:55 ` [PATCHv9 1/3] " Alexandre Courbot
2012-11-17 11:38 ` Anton Vorontsov
2012-11-19 2:29 ` Alex Courbot
2012-11-19 2:32 ` Anton Vorontsov
2012-11-20 14:48 ` Tomi Valkeinen
2012-11-21 1:56 ` Alex Courbot
2012-11-21 8:13 ` Tomi Valkeinen
2012-11-21 8:32 ` Alex Courbot
2012-11-21 8:48 ` Tomi Valkeinen
2012-11-21 10:00 ` Alex Courbot
2012-11-22 13:01 ` Grant Likely
2012-11-20 21:54 ` Grant Likely
2012-11-21 1:31 ` Mark Brown
2012-11-21 16:44 ` Grant Likely
2012-11-22 8:57 ` Linus Walleij
2012-11-22 9:55 ` Alexandre Courbot
2012-11-23 1:44 ` Mark Brown
2012-11-21 4:23 ` Alex Courbot
2012-11-21 11:06 ` Tomi Valkeinen
2012-11-21 11:40 ` Thierry Reding
2012-11-21 12:04 ` Tomi Valkeinen
2012-11-21 13:00 ` Thierry Reding
2012-11-21 13:32 ` Tomi Valkeinen
2012-11-21 15:02 ` Alexandre Courbot
2012-11-21 15:12 ` Thierry Reding
2012-11-22 2:01 ` Alexandre Courbot
2012-11-22 2:06 ` Mark Brown
2012-11-22 3:09 ` Alexandre Courbot
2012-11-22 13:39 ` Grant Likely
2012-11-27 15:19 ` Laurent Pinchart
2012-11-27 15:08 ` Laurent Pinchart
2012-11-27 15:19 ` Tomi Valkeinen [this message]
2012-11-27 15:37 ` Laurent Pinchart
2012-11-27 16:46 ` Mark Brown
2012-11-27 14:47 ` Laurent Pinchart
2012-11-22 13:39 ` Grant Likely
2012-11-22 21:40 ` Thierry Reding
2012-11-26 11:49 ` Alex Courbot
2012-11-26 15:34 ` Grant Likely
2012-11-17 10:55 ` [PATCHv9 2/3] pwm_backlight: use power sequences Alexandre Courbot
2012-11-17 10:55 ` [PATCHv9 3/3] Take maintainership of " Alexandre Courbot
2012-11-20 21:58 ` [PATCHv9 0/3] Runtime Interpreted Power Sequences Grant Likely
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