Re: [PATCH 2/5] ARM: dts: add Samsung's exynos4412-based p4note boards

From: Martin Juecker <martin.juecker@gmail.com>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: linux-samsung-soc@vger.kernel.org, kgene@kernel.org,
	devicetree@vger.kernel.org, Krzysztof Kozlowski <krzk@kernel.org>
Subject: Re: [PATCH 2/5] ARM: dts: add Samsung's exynos4412-based p4note boards
Date: Tue, 3 Nov 2020 11:38:56 +0100	[thread overview]
Message-ID: <20201103103856.GA7770@adroid> (raw)
In-Reply-To: <0af4946e-a573-ad5a-5558-de439d49434f@samsung.com>

On Tue, Nov 03, 2020 at 10:51:08AM +0100, Marek Szyprowski wrote:
> Hi Martin,
> 
> On 02.11.2020 22:21, Martin Juecker wrote:
> > > ...
> >>> +
> >>> +&fimd {
> >>> +	pinctrl-0 = <&lcd_clk &lcd_data24 &pwm1_out>;
> >>> +	pinctrl-names = "default";
> >>> +	status = "okay";
> >>> +
> >>> +	display-timings {
> >>> +		timing0 {
> >>> +			clock-frequency = <66666666>;
> >>> +			hactive = <1280>;
> >>> +			vactive = <800>;
> >>> +			hfront-porch = <18>;
> >>> +			hback-porch = <36>;
> >>> +			hsync-len = <16>;
> >>> +			vback-porch = <16>;
> >>> +			vfront-porch = <4>;
> >>> +			vsync-len = <3>;
> >>> +			hsync-active = <1>;
> >>> +		};
> >>> +	};
> >> What happened with Marek's comment about this?
> >>
> > Should have mentioned it in the introduction mail. I had a look at the
> > simple panel driver and it's not enough for the display in the p4note. I
> > asked Marek in IRC whether it's ok to have this in a separate patch set
> > to have a fully working display and he agreed.
> 
> Yes, I agreed that the display can be added later in a separate patch. 
> However in such case I would simply remove the whole fimd node now. 
> Without a panel it is a bit useless imho. With a proper panel driver you 
> will also get rid of the timings subnode, so there is no point adding it 
> now.
>

Removing the fimd node (or the display timings) would break the DRM and
display output though. The display is working but missing proper GPIO
handling and the possibility to adjust brightness right now. As it is
connected to the LCD power domain, it's still turning on and off as
expected as it is setup by the bootloader. I know this isn't a great
solution, but I'm already working on the LCD driver. Not sure when it
will be done though.

The display timings are read in exynos_drm_dpi.c in the exynos_dpi_probe
method. As far as I understand, you can either provide the timings in
the fimd node itself or in a connected panel.

If this is not intended, I can of course remove the configuration.

> Best regards
> 
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
> 

Cheers
Martin