Re: [PATCH] drm/i915: Add missing MacBook Pro models with dual channel LVDS

[Lukas Wunner <lukas@wunner.de>]

Hi Jani,

> I think this begs the question, why don't we assume dual link lvds when
> we know the native mode of the panel necessitates it?

Yes that's a great idea, that way we can avoid hardcoding the 17" models.
Coming up in a separate e-mail is a new version of the patch.

Single channel LVDS maxes out at 112 MHz, according to section 2.3
of this document:
https://01.org/linuxgraphics/sites/default/files/documentation/ivb_ihd_os_vol3_part4.pdf

The resolution of the 17" models -- 1920x1200 -- always needs more
bandwidth than 112 MHz (at 60 Hz it's 193 MHz), thus requires
dual channels.

The 15" models are a bit more complicated: By default they shipped
with 1440x900, that's 106 MHz so single channel LVDS would be
sufficient. As a BTO option however they were available with
1680x1050, that's 119 MHz and requires dual channels.

It turns out Apple apparently used dual channels on *both* 15"
versions, presumably to reduce the number of different parts,
i.e. use identical mainboards and display cabling on both
versions and the only differing component is the panel.

E.g. the Chi Mei N154C6-L04 panel with 1440x900...
http://www.ebay.com/itm/-/400690878560
... is a replacement panel for all "A1286" models, and that model
number encompasses the MacBookPro6,2 / 8,2 / 9,1...
http://www.everymac.com/ultimate-mac-lookup/?search_keywords=A1286
... and page 17 of the panel's datasheet shows it's driven with
dual channel LVDS:
http://www.taopanel.com/chimei/datasheet/N154C6-L04.pdf

Those three 15" models, MacBookPro6,2 / 8,2 / 9,1, are the only
ones with i915 graphics and dual channel LVDS, so that list should
be complete. And the 8,2 is already in intel_lvds.c.

Tested on a MacBookPro9,1 with 1680x1050.

Kind regards,

Lukas
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