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drm/i915/cdclk: Document CDCLK update methods

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Add a bit of documentation to briefly explain the methods
by which we can change the CDCLK frequency.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240207013334.29606-5-ville.syrjala@linux.intel.com
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
This commit is contained in:
Ville Syrjälä 2024-02-07 03:33:34 +02:00
parent c0151c695f
commit 79e2ea2eaa
1 changed files with 9 additions and 0 deletions
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9
drivers/gpu/drm/i915/display/intel_cdclk.c
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@ -63,6 +63,15 @@
* DMC will not change the active CDCLK frequency however, so that part * DMC will not change the active CDCLK frequency however, so that part
* will still be performed by the driver directly. * will still be performed by the driver directly.
* *
* Several methods exist to change the CDCLK frequency, which ones are
* supported depends on the platform:
* - Full PLL disable + re-enable with new VCO frequency. Pipes must be inactive.
* - CD2X divider update. Single pipe can be active as the divider update
* can be synchronized with the pipe's start of vblank.
* - Crawl the PLL smoothly to the new VCO frequency. Pipes can be active.
* - Squash waveform update. Pipes can be active.
* - Crawl and squash can also be done back to back. Pipes can be active.
*
* RAWCLK is a fixed frequency clock, often used by various auxiliary * RAWCLK is a fixed frequency clock, often used by various auxiliary
* blocks such as AUX CH or backlight PWM. Hence the only thing we * blocks such as AUX CH or backlight PWM. Hence the only thing we
* really need to know about RAWCLK is its frequency so that various * really need to know about RAWCLK is its frequency so that various