[coreboot-gerrit] Patch merged into coreboot/master: i945/gma.c: use linux code to calculate divisors

[gerrit at coreboot.org]

the following patch was just integrated into master:
commit 7dfc8a5ebdf6b272de4373da945d756eadcf2786
Author: Arthur Heymans <arthur at aheymans.xyz>
Date:   Fri Sep 2 22:35:32 2016 +0200

    i945/gma.c: use linux code to calculate divisors
    
    The code to compute n, m1, m2, p1 divisors is not correct in coreboot and
    on some targets hits a working mode at lower refresh rate, which is why
    display is working on some targets.
    
    The divisors must be such "refclk * (5 * (m1 + 2) + (m2 + 2))/ (n + 2)
    / (p1 * p2)" is as close as possible to the target frequency (which
    is defined by the resolution and refresh rate).
    
    This patch also fixes the reference frequency.
    
    This patch reuses linux (4.1) code from drivers/gpu/drm/i915/intel_display.c
    to correctly compute divisors.
    
    The result is that some previously not working displays, like many
    displays found on the Lenovo T60 might work now.
    Some examples of T60 displays that were known to not work (in payload):
    Samsung LTN141XA-L01 (14.1" 1024x768)
    LG-Philips LP150X09 (15.1" 1024x768)
    IDtech N150U3-L01 (15.1" 1600x1200)
    IDtech IAQX10N (15.1" 2048x1536)
    Samsung LTN154X3-L0A (15.4" 1280x800)
    LG-Philips LP150E06-A5K4 (15.1" 1400x1050)
    
    Tested on T60 with 1024x786.
    
    Change-Id: I2c7f3bb0024ac005029eaebe3ecdc70c38ac777e
    Signed-off-by: Arthur Heymans <arthur at aheymans.xyz>
    Reviewed-on: https://review.coreboot.org/16504
    Tested-by: build bot (Jenkins)
    Reviewed-by: Martin Roth <martinroth at google.com>


See https://review.coreboot.org/16504 for details.

-gerrit