[PATCH 03/13 v4] drm/i915/intel_i2c: assign HDMI port D to pin pair 6

From: Daniel Kurtz
Date: Tue Mar 27 2012 - 14:38:25 EST

According to i915 documentation [1], "Port D" (DP/HDMI Port D) is
actually gmbus pin pair 6 (gmbus0.2:0 == 110b GPIOF), not 7 (111b).
Pin pair 7 is a reserved pair.

[1] Documentation for [DevSNB+] and [DevIBX], as found on

Section 2.2.2 lists the 6 gmbus ports (gpio pin pairs):
[ 5: HDMI/DPD, 4: HDMIB, 3: HDMI/DPC, 2: LVDS, 1: SSC, 0: VGA ] lists the GPIO registers to control these 6 ports. lists the mapping between 5 of these gmbus ports and the 3
Pin_Pair_Select bits (of the GMBUS0 register). This table is missing
HDMIB (port 101).

[DevIBX]: http://intellinuxgraphics.org/IHD_OS_Vol3_Part3r2.pdf
Section 2.2.2 lists the same 6 gmbus ports plus two 'reserved' gpio
ports. lists 8 GPIO registers... however, it says the size of the
block is 6x32, which implies that those 2 reserved GPIO registers
(GPIO_6 & GPIO_7) don't actually exist (or are irrelevant). lists the mapping between the 6 named gmbus ports and the 3
Pin_Pair_Select bits (of the GMBUS0 register). This table has HDMIB.

Note: the "reserved" and "disabled" pairs do not actually map to a
physical pair of pins, nor GPIO regs and shouldn't be initialized or used.
Fixing this is left for a later patch.

This bug had not been noticed earlier for two reasons:
1) Until recently, "gmbus" mode was disabled - all transfers actually
used "bit-bang" mode on GPIO port 5 (the "HDMI/DPD CTLDATA/CLK"
pair), at register 0x5024 (defined as GPIOF i915_reg.h).
Since this is the correct pair of pins for HDMI1, transfers succeed.

2) Even if gmbus mode is re-enabled, the first attempted transaction
will fail because it tries to use the wrong ("Reserved") pin pair.
However, the driver immediately falls back again to the bit-bang
method, which correctly uses GPIOF, so again, transfers succeed.

However, if gmbus mode is re-enabled and the GPIO fall-back mode is
disabled, then reading an attached monitor's EDID fail.

Signed-off-by: Daniel Kurtz <djkurtz@xxxxxxxxxxxx>
drivers/gpu/drm/i915/i915_reg.h | 6 +++---
drivers/gpu/drm/i915/intel_i2c.c | 4 ++--
2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index f3609f2..accd8ee 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -742,9 +742,9 @@
#define GMBUS_PORT_DPC 4 /* HDMIC */
#define GMBUS_PORT_DPB 5 /* SDVO, HDMIB */
- /* 6 reserved */
-#define GMBUS_PORT_DPD 7 /* HDMID */
-#define GMBUS_NUM_PORTS 8
+#define GMBUS_PORT_DPD 6 /* HDMID */
+#define GMBUS_PORT_RESERVED 7 /* 7 reserved */
+#define GMBUS_NUM_PORTS 8
#define GMBUS1 0x5104 /* command/status */
#define GMBUS_SW_CLR_INT (1<<31)
#define GMBUS_SW_RDY (1<<30)
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index e6c090b..9347281 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -148,8 +148,8 @@ intel_gpio_setup(struct intel_gmbus *bus, u32 pin)
- 0,
+ 0,
struct i2c_algo_bit_data *algo;

@@ -385,8 +385,8 @@ int intel_setup_gmbus(struct drm_device *dev)
- "reserved",
+ "reserved",
struct drm_i915_private *dev_priv = dev->dev_private;
int ret, i;

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