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drm/i915: Document BDW+ DRRS M/N programming requirements

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When reprogramming M/N live on BDW+ we must write the LINK_N
register last as it's the one that arms the double buffered
register update for all the M/N registers. Document this so
that we don't accidentally break things.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128103757.22461-18-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
Ville Syrjälä 2022-01-28 12:37:57 +02:00
parent 2efb4adf48
commit 19d36cfafa
1 changed files with 4 additions and 0 deletions
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4
drivers/gpu/drm/i915/display/intel_display.c
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@ -3152,6 +3152,10 @@ void intel_set_m_n(struct drm_i915_private *i915,
intel_de_write(i915, data_m_reg, TU_SIZE(m_n->tu) | m_n->data_m);
intel_de_write(i915, data_n_reg, m_n->data_n);
intel_de_write(i915, link_m_reg, m_n->link_m);
/*
* On BDW+ writing LINK_N arms the double buffered update
* of all the M/N registers, so it must be written last.
*/
intel_de_write(i915, link_n_reg, m_n->link_n);
}