Commit 79e2ea2e authored by Ville Syrjälä's avatar Ville Syrjälä
Browse files

drm/i915/cdclk: Document CDCLK update methods 



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

Signed-off-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240207013334.29606-5-ville.syrjala@linux.intel.com


Reviewed-by: default avatarGustavo Sousa <gustavo.sousa@intel.com>
parent c0151c69

drivers/gpu/drm/i915/display/intel_cdclk.c

+9 −0
Original line number Diff line number Diff line
@@ -63,6 +63,15 @@ 
 * DMC will not change the active CDCLK frequency however, so that part

 * 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

 * 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