From 0de009c900e7ebd21097797f723a40813e953879 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 5 Apr 2011 16:04:39 +0100 Subject: drm/i915/crt: Remove 0xa0 probe for VGA This is a moral revert of 6ec3d0c0e9c0c605696e91048eebaca7b0c36695. 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 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35904 Reported-and-tested-by: Riccardo Magliocchetti Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=32612 Signed-off-by: Chris Wilson Acked-by: Dave Airlie Signed-off-by: Keith Packard --- drivers/gpu/drm/i915/intel_crt.c | 20 -------------------- 1 file changed, 20 deletions(-) (limited to 'drivers/gpu') diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c index 8342259f316..d03fc05b39c 100644 --- a/drivers/gpu/drm/i915/intel_crt.c +++ b/drivers/gpu/drm/i915/intel_crt.c @@ -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; -- cgit v1.2.3-18-g5258