Re: [RFC PATCH v2 19/21] ARM: dts: exynos5250-arndale: add dsi and panel nodes

From: Tomi Valkeinen <tomi.valkeinen@ti.com>
To: Andrzej Hajda <a.hajda@samsung.com>
Cc: Inki Dae <inki.dae@samsung.com>,
	DRI mailing list <dri-devel@lists.freedesktop.org>,
	Mark Rutland <mark.rutland@arm.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-samsung-soc@vger.kernel.org"
	<linux-samsung-soc@vger.kernel.org>,
	Pawel Moll <pawel.moll@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Rob Herring <robh+dt@kernel.org>,
	Kumar Gala <galak@codeaurora.org>,
	Grant Likely <grant.likely@linaro.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [RFC PATCH v2 19/21] ARM: dts: exynos5250-arndale: add dsi and panel nodes
Date: Fri, 7 Mar 2014 16:36:59 +0200	[thread overview]
Message-ID: <5319D98B.4080709@ti.com> (raw)
In-Reply-To: <5319D4FC.5090703@samsung.com>

[-- Attachment #1: Type: text/plain, Size: 1968 bytes --]

On 07/03/14 16:17, Andrzej Hajda wrote:
> On 03/07/2014 02:28 PM, Tomi Valkeinen wrote:
> (...)
>> There are many possible connections from FIMD, some of them:
>> FIMD ---> RGB panel, external
>> FIMD ---> DSI, on SoC
>> FIMD ---> eDP, on SoC
>> FIMD ---> ImageEnhacer, on SoC
>> This sounds similar to OMAP, at least roughly.
>>
>>> In the first case port should be created.
>>> In other cases connection could be determined by presence/absence
>>> of specific nodes, so in fact the port can be optional, almost like in
>>> my proposal :)
>> Well, I think not.
>>
>> In the external encoder case, the ports are there, and they are used.
>> You just didn't specify them, and thus make the driver deduce them from
>> the DT.
>>
>> In the FIMD case, if the the RGB port is needed, you need to specify it
>> in the DT data, and it's used. If you only need, say, DSI, the RGB port
>> is not used and thus it doesn't need to be present in the DT data.
>>
>> It's fine to leave the port definition out if it is not used at all.
> On Exynos, DSI is in fact RGB/DSI encoder (or I80/DSI). DSI and RGB pins
> are connected to the same FIMD output. So from FIMD point of view
> RGB port is used in both cases.

I guessed as much, as it's the same on OMAP.

But I think it's still fine to have a port only for RGB panel. For the
RGB panel, you have pins on the SoC to which the RGB data goes to. The
RGB port in DT represents these pins. You don't have pins for the
FIMD->DSI case.

But as I said, it's fine to use ports for internal connections also if
it works for you.

I still don't like the idea of having the port as optional in DT for
cases where the port comes from the parent device. Sure, it removes some
lines from the DT, but I think it makes it more confusing. Especially as
I think it's a very rare case where you could use that optional format,
as usually you will have some properties in the endpoint node.

 Tomi

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 901 bytes --]