Commit 0de009c9 authored Apr 05, 2011 by Chris Wilson Committed by Keith Packard Apr 05, 2011

drm/i915/crt: Remove 0xa0 probe for VGA



This is a moral revert of 6ec3d0c0.

Following the fix to reset the GMBUS controller after a NAK, we finally
utilize the 0xa0 probe for a CRT connection. And discover that the code
is broken. Shock.

There are a number of issues, but following a key insight from Dave
Airlie, that 0xA0 is an invalid address on a 7-bit bus (though not if we
were to enable 10-bit addressing), and would look like the EDID port
0x50, it is possible to see where the confusion starts.

In short, a write to 0xA0 is accepted by the GMBUS controller which we
interpreted as meaning the existence of a connection (a slave on the
other end of the wire ACKing the write). That was false.

During testing with a broken GMBUS implementation, which never reset an
earlier NAK, this test always reported a NAK and so we proceeded on to
the next test.

Reported-and-tested-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35904


Reported-and-tested-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=32612


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Keith Packard <keithp@keithp.com>

parent 7f58aabc

drivers/gpu/drm/i915/intel_crt.c

+0 −20

Original line number	Diff line number	Diff line
		@@ -269,21 +269,6 @@ static bool intel_crt_detect_hotplug(struct drm_connector *connector)
		return ret;
		}

		static bool intel_crt_ddc_probe(struct drm_i915_private *dev_priv, int ddc_bus)
		{
		u8 buf;
		struct i2c_msg msgs[] = {
		{
		.addr = 0xA0,
		.flags = 0,
		.len = 1,
		.buf = &buf,
		},
		};
		/* DDC monitor detect: Does it ACK a write to 0xA0? */
		return i2c_transfer(&dev_priv->gmbus[ddc_bus].adapter, msgs, 1) == 1;
		}

		static bool intel_crt_detect_ddc(struct drm_connector *connector)
		{
		struct intel_crt *crt = intel_attached_crt(connector);
		@@ -293,11 +278,6 @@ static bool intel_crt_detect_ddc(struct drm_connector *connector)
		if (crt->base.type != INTEL_OUTPUT_ANALOG)
		return false;

		if (intel_crt_ddc_probe(dev_priv, dev_priv->crt_ddc_pin)) {
		DRM_DEBUG_KMS("CRT detected via DDC:0xa0\n");
		return true;
		}

		if (intel_ddc_probe(&crt->base, dev_priv->crt_ddc_pin)) {
		struct edid *edid;
		bool is_digital = false;