Attachment 121460 Details for Bug 93956 – Patch to fix i2c for passive adapters

[patch] Patch to fix i2c for passive adapters

0001-drm-i915-Fix-DDC-probe-for-passive-adapters.patch (text/plain), 4.25 KB, created by Jim Bride on 2016-02-02 15:36:45 UTC

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Creator: Jim Bride

Created: 2016-02-02 15:36:45 UTC

Size: 4.25 KB

patch

obsolete

>From 3f5f1554ee715639e78d9be87623ee82772537e0 Mon Sep 17 00:00:00 2001
>From: Jani Nikula <jani.nikula@intel.com>
>Date: Tue, 2 Jun 2015 19:21:15 +0300
>Subject: [PATCH] drm/i915: Fix DDC probe for passive adapters
>MIME-Version: 1.0
>Content-Type: text/plain; charset=UTF-8
>Content-Transfer-Encoding: 8bit
>
>Passive DP->DVI/HDMI dongles on DP++ ports show up to the system as HDMI
>devices, as they do not have a sink device in them to respond to any AUX
>traffic. When probing these dongles over the DDC, sometimes they will
>NAK the first attempt even though the transaction is valid and they
>support the DDC protocol. The retry loop inside of
>drm_do_probe_ddc_edid() would normally catch this case and try the
>transaction again, resulting in success.
>
>That, however, was thwarted by the fix for [1]:
>
>commit 9292f37e1f5c79400254dca46f83313488093825
>Author: Eugeni Dodonov <eugeni.dodonov@intel.com>
>Date:   Thu Jan 5 09:34:28 2012 -0200
>
>    drm: give up on edid retries when i2c bus is not responding
>
>This added code to exit immediately if the return code from the
>i2c_transfer function was -ENXIO in order to reduce the amount of time
>spent in waiting for unresponsive or disconnected devices. That was
>possible because the underlying i2c bit banging algorithm had retries of
>its own (which, of course, were part of the reason for the bug the
>commit fixes).
>
>Since its introduction in
>
>commit f899fc64cda8569d0529452aafc0da31c042df2e
>Author: Chris Wilson <chris@chris-wilson.co.uk>
>Date:   Tue Jul 20 15:44:45 2010 -0700
>
>    drm/i915: use GMBUS to manage i2c links
>
>we've been flipping back and forth enabling the GMBUS transfers, but
>we've settled since then. The GMBUS implementation does not do any
>retries, however, bailing out of the drm_do_probe_ddc_edid() retry loop
>on first encounter of -ENXIO. This, combined with Eugeni's commit, broke
>the retry on -ENXIO.
>
>Retry GMBUS once on -ENXIO on first message to mitigate the issues with
>passive adapters.
>
>This patch is based on the work, and commit message, by Todd Previte
><tprevite@gmail.com>.
>
>[1] https://bugs.freedesktop.org/show_bug.cgi?id=41059
>
>v2: Don't retry if using bit banging.
>
>v3: Move retry within gmbux_xfer, retry only on first message.
>
>v4: Initialize GMBUS0 on retry (Ville).
>
>v5: Take index reads into account (Ville).
>
>Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85924
>Cc: Todd Previte <tprevite@gmail.com>
>Cc: stable@vger.kernel.org
>Tested-by: Oliver Grafe <oliver.grafe@ge.com> (v2)
>Tested-by: Jim Bride <jim.bride@linux.intel.com>
>Reviewed-by: Ville SyrjÃ¤lÃ¤ <ville.syrjala@linux.intel.com>
>Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>---
> drivers/gpu/drm/i915/intel_i2c.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
>index 56e437e..ae62800 100644
>--- a/drivers/gpu/drm/i915/intel_i2c.c
>+++ b/drivers/gpu/drm/i915/intel_i2c.c
>@@ -435,7 +435,7 @@ gmbus_xfer(struct i2c_adapter *adapter,
> 					       struct intel_gmbus,
> 					       adapter);
> 	struct drm_i915_private *dev_priv = bus->dev_priv;
>-	int i, reg_offset;
>+	int i = 0, inc, try = 0, reg_offset;
> 	int ret = 0;
> 
> 	intel_aux_display_runtime_get(dev_priv);
>@@ -448,12 +448,14 @@ gmbus_xfer(struct i2c_adapter *adapter,
> 
> 	reg_offset = dev_priv->gpio_mmio_base;
> 
>+retry:
> 	I915_WRITE(GMBUS0 + reg_offset, bus->reg0);
> 
>-	for (i = 0; i < num; i++) {
>+	for (; i < num; i += inc) {
>+		inc = 1;
> 		if (gmbus_is_index_read(msgs, i, num)) {
> 			ret = gmbus_xfer_index_read(dev_priv, &msgs[i]);
>-			i += 1;  /* set i to the index of the read xfer */
>+			inc = 2; /* an index read is two msgs */
> 		} else if (msgs[i].flags & I2C_M_RD) {
> 			ret = gmbus_xfer_read(dev_priv, &msgs[i], 0);
> 		} else {
>@@ -525,6 +527,18 @@ clear_err:
> 			 adapter->name, msgs[i].addr,
> 			 (msgs[i].flags & I2C_M_RD) ? 'r' : 'w', msgs[i].len);
> 
>+	/*
>+	 * Passive adapters sometimes NAK the first probe. Retry the first
>+	 * message once on -ENXIO for GMBUS transfers; the bit banging algorithm
>+	 * has retries internally. See also the retry loop in
>+	 * drm_do_probe_ddc_edid, which bails out on the first -ENXIO.
>+	 */
>+	if (ret == -ENXIO && i == 0 && try++ == 0) {
>+		DRM_DEBUG_KMS("GMBUS [%s] NAK on first message, retry\n",
>+			      adapter->name);
>+		goto retry;
>+	}
>+
> 	goto out;
> 
> timeout:
>-- 
>2.5.0
>

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