drm/i915/adl_p: Tx escape clock with DSI
Today when the DSI controller is paired with the Combo-PHY it uses the high-speed (HS) Word clock for its low power (LP) transmit PPI communication to the DPHY. The interface signaling only changes state at an Escape clock frequency (i.e. its effectively running on a virtual Tx Escape clock that is controlled by counters w/in the controller), but all the interface flops are running off the HS clock. This has the following drawbacks: * It is a deviation from the PPI spec which assumes signaling is running on a physical Escape clock * The PV timings are over constrained (HS timed to 312.5MHz vs. an Escape clock of 20MHz max) This feature is proposing to change the LP Tx communication between the controller and the DPHY from a virtual Tx Escape clock to a physical clock. To do this we need to program two "M" divisors. One for the usual DSI_ESC_CLK_DIV and DPHY_ESC_CLK_DIV register and one for MIPIO_DWORD8. For DSI_ESC_CLK_DIV and DPHY_ESC_CLK_DIV registers the "M" is calculated as following Nt = ceil(f_link/160) (theoretical word clock) Nact = max[3, Nt + (Nt + 1)%2] (actual word clock) M = Nact * 8 For MIPIO_DWORD8 register, the divisor "M" is calculated as following M = (Nact - 1)/2 BSpec: 55171 Cc: Vandita Kulkarni <vandita.kulkarni@intel.com> Signed-off-by: Mika Kahola <mika.kahola@intel.com> Signed-off-by: Clinton Taylor <Clinton.A.Taylor@intel.com> Signed-off-by: Matt Roper <matthew.d.roper@intel.com> Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20210519000625.3184321-11-lucas.demarchi@intel.com
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