ed06efb801
There was a integer wraparound when mode_clock became too high,
and we didn't correct for the FEC overhead factor when dividing,
with the calculations breaking at HBR3.
As a result our calculated bpp was way too high, and the link width
limitation never came into effect.
Print out the resulting bpp calcululations as a sanity check, just
in case we ever have to debug it later on again.
We also used the wrong factor for FEC. While bspec mentions 2.4%,
all the calculations use 1/0.972261, and the same ratio should be
applied to data M/N as well, so use it there when FEC is enabled.
This fixes the FIFO underrun we are seeing with FEC enabled.
Changes since v2:
- Handle fec_enable in intel_link_compute_m_n, so only data M/N is adjusted. (Ville)
- Fix initial hardware readout for FEC. (Ville)
Changes since v3:
- Remove bogus fec_to_mode_clock. (Ville)
Changes since v4:
- Use the correct register for icl. (Ville)
- Split hw readout to a separate patch.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: d9218c8f6cf4 ("drm/i915/dp: Add helpers for Compressed BPP and Slice Count for DSC")
Cc: <stable@vger.kernel.org> # v5.0+
Cc: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190925082110.17439-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.