drm/tegra: dpaux: Retry on transfer size mismatch

When a transfer didn't complete transmission of the requested number of
bytes, signal that the transaction should be retried.

Signed-off-by: Thierry Reding <treding@nvidia.com>

diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
index 4a35a6e0e2aa25de2a2c39f5fd466287564701fa..819fdd9b4413b175ccfd493e6b13d48bfff652f9 100644 (file)
--- a/drivers/gpu/drm/tegra/dpaux.c
+++ b/drivers/gpu/drm/tegra/dpaux.c
@@ -121,6 +121,7 @@ static ssize_t tegra_dpaux_transfer(struct drm_dp_aux *aux,
        struct tegra_dpaux *dpaux = to_dpaux(aux);
        unsigned long status;
        ssize_t ret = 0;
+       u8 reply = 0;
        u32 value;
 
        /* Tegra has 4x4 byte DP AUX transmit and receive FIFOs. */
@@ -215,23 +216,23 @@ static ssize_t tegra_dpaux_transfer(struct drm_dp_aux *aux,
 
        switch ((value & DPAUX_DP_AUXSTAT_REPLY_TYPE_MASK) >> 16) {
        case 0x00:
-               msg->reply = DP_AUX_NATIVE_REPLY_ACK;
+               reply = DP_AUX_NATIVE_REPLY_ACK;
                break;
 
        case 0x01:
-               msg->reply = DP_AUX_NATIVE_REPLY_NACK;
+               reply = DP_AUX_NATIVE_REPLY_NACK;
                break;
 
        case 0x02:
-               msg->reply = DP_AUX_NATIVE_REPLY_DEFER;
+               reply = DP_AUX_NATIVE_REPLY_DEFER;
                break;
 
        case 0x04:
-               msg->reply = DP_AUX_I2C_REPLY_NACK;
+               reply = DP_AUX_I2C_REPLY_NACK;
                break;
 
        case 0x08:
-               msg->reply = DP_AUX_I2C_REPLY_DEFER;
+               reply = DP_AUX_I2C_REPLY_DEFER;
                break;
        }
 
@@ -239,14 +240,24 @@ static ssize_t tegra_dpaux_transfer(struct drm_dp_aux *aux,
                if (msg->request & DP_AUX_I2C_READ) {
                        size_t count = value & DPAUX_DP_AUXSTAT_REPLY_MASK;
 
-                       if (WARN_ON(count != msg->size))
-                               count = min_t(size_t, count, msg->size);
+                       /*
+                        * There might be a smarter way to do this, but since
+                        * the DP helpers will already retry transactions for
+                        * an -EBUSY return value, simply reuse that instead.
+                        */
+                       if (count != msg->size) {
+                               ret = -EBUSY;
+                               goto out;
+                       }
 
                        tegra_dpaux_read_fifo(dpaux, msg->buffer, count);
                        ret = count;
                }
        }
 
+       msg->reply = reply;
+
+out:
        return ret;
 }