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Jani Nikula 9a86cda07a drm/i915/dp: reduce link M/N parameters
Several major vendor USB-C->HDMI converters, in particular the DA200,
fail to recover a 5.4 GHz 1 lane signal if the link N is greater than
0x80000.

The link M and N depend on the pixel clock and link clock ratio. With
current code link N exceeds 0x80000 only when link clock >= 540000
kHz. Except for the eDP intermediate link clocks, at least the four
least significant bits are always zero. Just one bit shift right would
be enough to bring even the DP 1.4 810000 kHz link clock under 0x80000
link N. The pixel clock for modes that require a link clock >= 540000
kHz would also have several least significant bits zero. Unless the user
provides a mode with an odd pixel clock value, we can reduce the numbers
to reach the goal, with no loss in precision.

The DP spec even mentions sources making choices that "allow for static
and relatively small Mvid and Nvid values", thus reducing the link M/N
regardless of the sink in question seems justified.

Everything here is based on the work and information gathered by Clint
Taylor <clinton.a.taylor@intel.com>. This is just an iteration to reduce
the parameters regardless of lane count, link rate, or sink.

Reference: http://patchwork.freedesktop.org/patch/msgid/1490225256-11667-1-git-send-email-clinton.a.taylor@intel.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93578
Tested-by: Mads <mads@ab3.no>
Tested-by: PJ <foobar@pjmodos.net>
Tested-by: François Guerraz <kubrick@fgv6.net>
Tested-by: Lev Popov <leo@nabam.net>
Tested-by: Igor Krivenko <igor.s.krivenko@gmail.com>
Tested-by: Clint Taylor <clinton.a.taylor@intel.com>
Reviewed-by: Clint Taylor <clinton.a.taylor@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1490614405-23337-1-git-send-email-jani.nikula@intel.com
History 2017-03-28 18:18:23 +03:00
arch Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
block blk-mq: don't complete un-started request in timeout handler 2017-03-22 08:03:35 -06:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto net: Work around lockdep limitation in sockets that use sockets 2017-03-09 18:23:27 -08:00
Documentation Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
drivers drm/i915/dp: reduce link M/N parameters 2017-03-28 18:18:23 +03:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs driver core fix for 4.11-rc4 2017-03-26 11:05:42 -07:00
include Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
init Change get_random_{int,log} to use the CRNG used by /dev/urandom and 2017-03-11 09:08:47 -08:00
ipc Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
kernel Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
lib mm: convert generic code to 5-level paging 2017-03-09 11:48:47 -08:00
mm mm, swap: Remove WARN_ON_ONCE() in free_swap_slot() 2017-03-21 14:13:19 -07:00
net A fix for a writeback deadlock caused by a GFP_KERNEL allocation on the 2017-03-24 14:35:39 -07:00
samples Merge branch 'rebased-statx' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-03-03 11:38:56 -08:00
scripts Linux 4.11-rc3 2017-03-23 12:05:13 +10:00
security Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
sound ALSA: hda - Adding a group of pin definition to fix headset problem 2017-03-23 09:39:55 +01:00
tools Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
usr kbuild: initramfs cleanup, set target from Kconfig 2017-01-05 09:40:16 -08:00
virt KVM: arm/arm64: VGIC: Fix command handling while ITS being disabled 2017-03-07 15:44:08 +00:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap mailmap: add codeaurora.org names for nameless email commits 2017-01-10 18:31:55 -08:00
COPYING [PATCH] update FSF address in COPYING 2005-09-10 10:06:29 -07:00
CREDITS MAINTAINERS: Remove old e-mail address 2017-02-13 12:24:56 -05:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig kbuild: migrate all arch to the kconfig mainmenu upgrade 2010-09-19 22:54:11 -04:00
MAINTAINERS Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
Makefile Linux 4.11-rc4 2017-03-26 14:15:16 -07:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.