Merge branches 'arm/rockchip', 'arm/exynos', 'arm/smmu', 'x86/vt-d', 'x86/amd', ...

[sfrench/cifs-2.6.git] / drivers / gpu / drm / i915 / intel_i2c.c

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 56e437e3158021a09641d188affc6129f0b1eda8..ae628001fd97873b67f99fb0128167858948afe6 100644 (file)
--- 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: