[PATCH v6 15/15] drm/bridge: tc358767: Add support for address-only I2C transfers

[Andrey Smirnov]

Transfer size of zero means a request to do an address-only
transfer. Since the HW support this, we probably shouldn't be just
ignoring such requests. While at it allow DP_AUX_I2C_MOT flag to pass
through, since it is supported by the HW as well.

Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com>
Reviewed-by: Andrzej Hajda <a.ha...@samsung.com>
Cc: Andrzej Hajda <a.ha...@samsung.com>
Cc: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
Cc: Tomi Valkeinen <tomi.valkei...@ti.com>
Cc: Andrey Gusakov <andrey.gusa...@cogentembedded.com>
Cc: Philipp Zabel <p.za...@pengutronix.de>
Cc: Cory Tusar <cory.tu...@zii.aero>
Cc: Chris Healy <cphe...@gmail.com>
Cc: Lucas Stach <l.st...@pengutronix.de>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-ker...@vger.kernel.org
---
 drivers/gpu/drm/bridge/tc358767.c | 42 +++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358767.c 
b/drivers/gpu/drm/bridge/tc358767.c
index 3f8a15390813..7b8e19d6cf29 100644
--- a/drivers/gpu/drm/bridge/tc358767.c
+++ b/drivers/gpu/drm/bridge/tc358767.c
@@ -145,6 +145,8 @@
 
 /* AUX channel */
 #define DP0_AUXCFG0            0x0660
+#define DP0_AUXCFG0_BSIZE      GENMASK(11, 8)
+#define DP0_AUXCFG0_ADDR_ONLY  BIT(4)
 #define DP0_AUXCFG1            0x0664
 #define AUX_RX_FILTER_EN               BIT(16)
 
@@ -326,6 +328,18 @@ static int tc_aux_read_data(struct tc_data *tc, void 
*data, size_t size)
        return size;
 }
 
+static u32 tc_auxcfg0(struct drm_dp_aux_msg *msg, size_t size)
+{
+       u32 auxcfg0 = msg->request;
+
+       if (size)
+               auxcfg0 |= FIELD_PREP(DP0_AUXCFG0_BSIZE, size - 1);
+       else
+               auxcfg0 |= DP0_AUXCFG0_ADDR_ONLY;
+
+       return auxcfg0;
+}
+
 static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
                               struct drm_dp_aux_msg *msg)
 {
@@ -335,9 +349,6 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
        u32 auxstatus;
        int ret;
 
-       if (size == 0)
-               return 0;
-
        ret = tc_aux_wait_busy(tc);
        if (ret)
                return ret;
@@ -348,9 +359,11 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
                break;
        case DP_AUX_NATIVE_WRITE:
        case DP_AUX_I2C_WRITE:
-               ret = tc_aux_write_data(tc, msg->buffer, size);
-               if (ret < 0)
-                       return ret;
+               if (size) {
+                       ret = tc_aux_write_data(tc, msg->buffer, size);
+                       if (ret < 0)
+                               return ret;
+               }
                break;
        default:
                return -EINVAL;
@@ -361,8 +374,7 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
        if (ret)
                return ret;
        /* Start transfer */
-       ret = regmap_write(tc->regmap, DP0_AUXCFG0,
-                          ((size - 1) << 8) | request);
+       ret = regmap_write(tc->regmap, DP0_AUXCFG0, tc_auxcfg0(msg, size));
        if (ret)
                return ret;
 
@@ -376,14 +388,22 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
 
        if (auxstatus & AUX_TIMEOUT)
                return -ETIMEDOUT;
-
-       size = FIELD_GET(AUX_BYTES, auxstatus);
+       /*
+        * For some reason address-only DP_AUX_I2C_WRITE (MOT), still
+        * reports 1 byte transferred in its status. To deal we that
+        * we ignore aux_bytes field if we know that this was an
+        * address-only transfer
+        */
+       if (size)
+               size = FIELD_GET(AUX_BYTES, auxstatus);
        msg->reply = FIELD_GET(AUX_STATUS, auxstatus);
 
        switch (request) {
        case DP_AUX_NATIVE_READ:
        case DP_AUX_I2C_READ:
-               return tc_aux_read_data(tc, msg->buffer, size);
+               if (size)
+                       return tc_aux_read_data(tc, msg->buffer, size);
+               break;
        }
 
        return size;
-- 
2.21.0