linux-kernel - Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support

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Message-ID: <510A1DAC.1070106@gmail.com>
Date:	Thu, 31 Jan 2013 15:30:52 +0800
From:	Mark Zhang <nvmarkzhang@...il.com>
To:	Alexandre Courbot <gnurou@...il.com>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Mark Zhang <markz@...dia.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"acourbot@...dia.com" <acourbot@...dia.com>
Subject: Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support

On 01/31/2013 02:36 PM, Alexandre Courbot wrote:
> On Thu, Jan 31, 2013 at 1:54 PM, Mark Zhang <nvmarkzhang@...il.com> wrote:
>> Display controller don't know whether the panel has EDID EEPROM but the
>> panel driver knows. So why we need to make display controller queries
>> EDID blindly? Since panel driver knows about all "video modes/panel
>> size" stuffs, why not we let it handle all these things?
> 
> The DC actually does know whether the connected panel supports EDID -
> in this case, the output node will have a property for the DDC bus,
> e.g.
> 
>         nvidia,ddc-i2c-bus = <&lcd_ddc>;
> 
> If no DDC bus is specified or if transfer fails, the DC driver can
> still query the panel driver for hardcoded modes.
> 

Strictly speaking, according to my understanding, "nvidia,ddc-i2c-bus"
means tegra has a hardware ddc channel, this doesn't mean we can get the
EDID from this DDC surely.

> Also passing a function pointer to get_modes() does not relief the DC
> driver from probing for the DDC bus. You will still have to handle
> both conditions (DDC bus present or not), the check will just be moved
> into your callback function.
> 

Yes. But panel driver decides whether the DDC probing is needed. If the
panel has an EEPROM, it can call the function which display controller
provides to do a DDC probing, it not, panel driver just ignores this
function pointer and return the hardcoded modes directly.

> Alex.
> 
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