[S] Change in libgfxinit[master]: hw-gfx-dp_info.adb: Fix reading `Aux_RD_Interval`

[Nico Huber (Code Review)]

Nico Huber has submitted this change. ( https://review.coreboot.org/c/libgfxinit/+/67445 )

Change subject: hw-gfx-dp_info.adb: Fix reading `Aux_RD_Interval`
......................................................................

hw-gfx-dp_info.adb: Fix reading `Aux_RD_Interval`

Starting with DP v1.4, the definition of DPCD address 0xe was updated
to include a new field. Bit 7 now indicates whether a DP receiver has
an Extended Receiver Capability field, so `Aux_RD_Interval` is now in
bits 6:0. This change is backwards compatible with older hardware, as
the defined values for `Aux_RD_Interval` range from 0 to 4, and bit 7
is always zero.

However, libgfxinit does not make sure the value is valid before using
it in calculations, so the `EQ_Delay` function may return an extremely
large value if bit 7 is set. To avoid this, add some masks to properly
obtain the value for `Aux_RD_Interval`.

Change-Id: If22d8dbc0517daeaa043ede30bf69e7a65ab154b
Signed-off-by: Angel Pons 
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/67445
Reviewed-by: Nico Huber 
Reviewed-by: Tim Wawrzynczak 
Tested-by: Nico Huber 
---
M common/hw-gfx-dp_info.adb
1 file changed, 28 insertions(+), 2 deletions(-)

Approvals:
  Nico Huber: Verified; Looks good to me, approved
  Tim Wawrzynczak: Looks good to me, approved

diff --git a/common/hw-gfx-dp_info.adb b/common/hw-gfx-dp_info.adb
index bf09933..392fee1 100644
--- a/common/hw-gfx-dp_info.adb
+++ b/common/hw-gfx-dp_info.adb
@@ -72,7 +72,7 @@
          Link.Receiver_Caps.TPS3_Supported     := (Data (2) and 16#40#) /= 0;
          Link.Receiver_Caps.Enhanced_Framing   := (Data (2) and 16#80#) /= 0;
          Link.Receiver_Caps.No_Aux_Handshake   := (Data (3) and 16#40#) /= 0;
-         Link.Receiver_Caps.Aux_RD_Interval    := Data (14);
+         Link.Receiver_Caps.Aux_RD_Interval    := Data (14) and 16#7f#;

pragma Debug (Debug.New_Line);
          pragma Debug (Debug.Put_Line ("DPCD:"));
@@ -82,7 +82,7 @@
          pragma Debug (Debug.Put_Reg8 ("  TPS3_Supported  ", Data (2) and 16#40#));
          pragma Debug (Debug.Put_Reg8 ("  Enhanced_Framing", Data (2) and 16#80#));
          pragma Debug (Debug.Put_Reg8 ("  No_Aux_Handshake", Data (3) and 16#40#));
-         pragma Debug (Debug.Put_Reg8 ("  Aux_RD_Interval ", Data (14)));
+         pragma Debug (Debug.Put_Reg8 ("  Aux_RD_Interval ", Data (14) and 16#7f#));
          pragma Debug (Debug.New_Line);
       end if;
    end Read_Caps;