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drm/i915: Add a brief description of the VLV display PHY internals

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Document the internal structure of the VLV display PHY a bit to help
people understand how the different register blocks relate to each
other.

v2: Add a bit more text
    Make it a DOC: comment, but leave the ascii art out since
    it would get mangled

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chon Ming Lee <chon.ming.lee@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Ville Syrjälä 2014-04-25 20:14:31 +03:00 committed by Daniel Vetter
parent 46470fc932
commit 0e76718923
2 changed files with 85 additions and 4 deletions
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4
Documentation/DocBook/drm.tmpl
View File

@ -2937,6 +2937,10 @@ int num_ioctls;</synopsis>
probing, so those sections fully apply.
</para>
</sect2>
<sect2>
<title>DPIO</title>
!Pdrivers/gpu/drm/i915/i915_reg.h DPIO
</sect2>
</sect1>
<sect1>

85
drivers/gpu/drm/i915/i915_reg.h
View File

@ -575,12 +575,89 @@ enum punit_power_well {
#define DSI_PLL_M1_DIV_MASK (0x1ff << 0)
#define CCK_DISPLAY_CLOCK_CONTROL 0x6b
/**
* DOC: DPIO
*
* VLV and CHV 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 the common lane corresponds to the pipe and
* the spline (PCS/TX) correponds 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
*
* Note: digital port B is DDI0, digital port C is DDI1,
* digital port D is DDI2
*/
/*
* DPIO - a special bus for various display related registers to hide behind
* Dual channel PHY (VLV/CHV)
* ---------------------------------
* | 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
* ---------------------------------
*
* DPIO is VLV only.
*
* Note: digital port B is DDI0, digital pot C is DDI1
* Single channel PHY (CHV)
* -----------------
* | CH0 |
* | CMN/PLL/REF |
* |---------------| Display PHY
* | PCS01 | PCS23 |
* |-------|-------|
* |TX0|TX1|TX2|TX3|
* -----------------
* | DDI2 | DP/HDMI port
* -----------------
*/
#define DPIO_DEVFN 0