[Intel-gfx] [PATCH v2 2/3] drm/i915: Add a brief description of the VLV display PHY internals
Ville Syrjälä
ville.syrjala at linux.intel.com
Wed May 21 10:49:47 CEST 2014
On Wed, May 21, 2014 at 04:31:37PM +0800, Lee, Chon Ming wrote:
> On 04/25 20:14, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >
> > 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 at linux.intel.com>
> > ---
> > Documentation/DocBook/drm.tmpl | 4 ++
> > drivers/gpu/drm/i915/i915_reg.h | 85 +++++++++++++++++++++++++++++++++++++++--
> > 2 files changed, 85 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
> > index 4a955b4..e361ccd 100644
> > --- a/Documentation/DocBook/drm.tmpl
> > +++ b/Documentation/DocBook/drm.tmpl
> > @@ -2942,6 +2942,10 @@ 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>
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index b6d5045..8e18e8f 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -566,12 +566,89 @@ enum punit_power_well {
> > #define DSI_PLL_M1_DIV_MASK (0x1ff << 0)
> > #define CCK_DISPLAY_CLOCK_CONTROL 0x6b
> >
> > -/*
> > - * DPIO - a special bus for various display related registers to hide behind
> > +/**
> > + * 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
> > *
> > - * DPIO is VLV only.
> > + * 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.
> > + *
>
>
> Do you want to add something like the PHY actually allow PLL CH0 to supply clock
> to both ports, same as PLL CH1. But this is something i915 not supported yet,
> for power saving purpose.
Maybe we can add the comment if and when we implement it.
I'm not even sure if we should implement it since it might lead to
blinking displays if we have to reroute the PLLs for active pipes.
Although maybe it's possible to swap over to the pipe's own PLL from
the shared case w/o blinking, but that would require special code
in the modeset path since we'd need to make sure we fire up the new
PLL first, then swap the PLLs, and only then can reprogram the old
PLL.
So unless the power savings are really significant I'm not sure anyone
will bother with this.
OTOH we already have potential display blinking due to the cdclk change
logic, so maybe we don't care that much.
>
> > + * 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
> > + */
> > +/*
> > + * Dual channel PHY (VLV/CHV)
> > + * ---------------------------------
> > + * | CH0 | CH1 |
> > + * | CMN/PLL/REF | CMN/PLL/REF |
>
> There is a AUX for both CH0 and CH1.
I left out AUX since the fact that it's part of the PHY isn't
really significant for us. I did mention it in the text.
>
> Other than this,
>
> Reviewed-by: Chon Ming Lee <chon.ming.lee at intel.com>
>
>
> > + * |---------------|---------------| Display PHY
> > + * | PCS01 | PCS23 | PCS01 | PCS23 |
> > + * |-------|-------|-------|-------|
> > + * |TX0|TX1|TX2|TX3|TX0|TX1|TX2|TX3|
> > + * ---------------------------------
> > + * | DDI0 | DDI1 | DP/HDMI ports
> > + * ---------------------------------
> > *
> > - * 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
> > #define DPIO_OPCODE_REG_WRITE 1
> > --
> > 1.8.3.2
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Ville Syrjälä
Intel OTC
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