drm/i915: Move DPIO phy documentation section to intel_dpio_phy.c

Move the DPIO phy documentation section to intel_dpio_phy.c, since that
is a more suitable place now that there is a source file dedicated for
those phys.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/55a2d38c15c06a8c5bce498b28decc03948f0224.1475770848.git-series.ander.conselvan.de.oliveira@intel.com

1 files changed, 91 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_dpio_phy.c b/drivers/gpu/drm/i915/intel_dpio_phy.c
index edf0cfd..6806296 100644
--- a/drivers/gpu/drm/i915/intel_dpio_phy.c
+++ b/drivers/gpu/drm/i915/intel_dpio_phy.c
@@ -23,6 +23,97 @@
 
 #include "intel_drv.h"
 
+/**
+ * DOC: DPIO
+ *
+ * VLV, CHV and BXT have slightly peculiar display PHYs for driving DP/HDMI
+ * ports. DPIO is the name given to such a display PHY. These PHYs
+ * don't follow the standard programming model using direct MMIO
+ * registers, and instead their registers must be accessed trough IOSF
+ * sideband. VLV has one such PHY for driving ports B and C, and CHV
+ * adds another PHY for driving port D. Each PHY responds to specific
+ * IOSF-SB port.
+ *
+ * Each display PHY is made up of one or two channels. Each channel
+ * houses a common lane part which contains the PLL and other common
+ * logic. CH0 common lane also contains the IOSF-SB logic for the
+ * Common Register Interface (CRI) ie. the DPIO registers. CRI clock
+ * must be running when any DPIO registers are accessed.
+ *
+ * In addition to having their own registers, the PHYs are also
+ * controlled through some dedicated signals from the display
+ * controller. These include PLL reference clock enable, PLL enable,
+ * and CRI clock selection, for example.
+ *
+ * Eeach channel also has two splines (also called data lanes), and
+ * each spline is made up of one Physical Access Coding Sub-Layer
+ * (PCS) block and two TX lanes. So each channel has two PCS blocks
+ * and four TX lanes. The TX lanes are used as DP lanes or TMDS
+ * data/clock pairs depending on the output type.
+ *
+ * Additionally the PHY also contains an AUX lane with AUX blocks
+ * for each channel. This is used for DP AUX communication, but
+ * this fact isn't really relevant for the driver since AUX is
+ * controlled from the display controller side. No DPIO registers
+ * need to be accessed during AUX communication,
+ *
+ * Generally on VLV/CHV the common lane corresponds to the pipe and
+ * the spline (PCS/TX) corresponds to the port.
+ *
+ * For dual channel PHY (VLV/CHV):
+ *
+ *  pipe A == CMN/PLL/REF CH0
+ *
+ *  pipe B == CMN/PLL/REF CH1
+ *
+ *  port B == PCS/TX CH0
+ *
+ *  port C == PCS/TX CH1
+ *
+ * This is especially important when we cross the streams
+ * ie. drive port B with pipe B, or port C with pipe A.
+ *
+ * For single channel PHY (CHV):
+ *
+ *  pipe C == CMN/PLL/REF CH0
+ *
+ *  port D == PCS/TX CH0
+ *
+ * On BXT the entire PHY channel corresponds to the port. That means
+ * the PLL is also now associated with the port rather than the pipe,
+ * and so the clock needs to be routed to the appropriate transcoder.
+ * Port A PLL is directly connected to transcoder EDP and port B/C
+ * PLLs can be routed to any transcoder A/B/C.
+ *
+ * Note: DDI0 is digital port B, DD1 is digital port C, and DDI2 is
+ * digital port D (CHV) or port A (BXT). ::
+ *
+ *
+ *     Dual channel PHY (VLV/CHV/BXT)
+ *     ---------------------------------
+ *     |      CH0      |      CH1      |
+ *     |  CMN/PLL/REF  |  CMN/PLL/REF  |
+ *     |---------------|---------------| Display PHY
+ *     | PCS01 | PCS23 | PCS01 | PCS23 |
+ *     |-------|-------|-------|-------|
+ *     |TX0|TX1|TX2|TX3|TX0|TX1|TX2|TX3|
+ *     ---------------------------------
+ *     |     DDI0      |     DDI1      | DP/HDMI ports
+ *     ---------------------------------
+ *
+ *     Single channel PHY (CHV/BXT)
+ *     -----------------
+ *     |      CH0      |
+ *     |  CMN/PLL/REF  |
+ *     |---------------| Display PHY
+ *     | PCS01 | PCS23 |
+ *     |-------|-------|
+ *     |TX0|TX1|TX2|TX3|
+ *     -----------------
+ *     |     DDI2      | DP/HDMI port
+ *     -----------------
+ */
+
 bool bxt_ddi_phy_is_enabled(struct drm_i915_private *dev_priv,
 			    enum dpio_phy phy)
 {