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path: root/drivers/gpu/drm/i915/intel_i2c.c
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Diffstat (limited to 'drivers/gpu/drm/i915/intel_i2c.c')
-rw-r--r--drivers/gpu/drm/i915/intel_i2c.c20
1 files changed, 17 insertions, 3 deletions
diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 56e437e31580..ae628001fd97 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: