[PATCH v2 7/7] drm/bridge: tc358768: Add support for long command tx via video buffer

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

TC358768 has two ways to send DSI commands: 1) buffer the payload data
into registers (DSICMD_WDx), which supports up to 8 bytes of payload, 2)
buffer the payload data into the video buffer, which supports up to 1024
bytes of payload.

The driver currently supports method 1).

Add support for transmitting long DSI commands (more than 8 bytes, up to
1024 bytes) using the video buffer. This mode can only be used before
the actual video transmission is enabled, i.e. the initial configuration.

Original version from Parth Pancholi <parth.pancholi@toradex.com>

Tested-by: João Paulo Gonçalves <joao.goncalves@toradex.com> # Toradex Verdin AM62
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
 drivers/gpu/drm/bridge/tc358768.c | 79 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 70 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index e1ed4003b3c5..e0b5a4b5abbe 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -45,6 +45,9 @@
 
 /* Debug (16-bit addressable) */
 #define TC358768_VBUFCTRL		0x00E0
+#define TC358768_VBUFCTRL_VBUF_EN	BIT(15)
+#define TC358768_VBUFCTRL_TX_EN		BIT(14)
+#define TC358768_VBUFCTRL_MASK		BIT(13)
 #define TC358768_DBG_WIDTH		0x00E2
 #define TC358768_DBG_VBLANK		0x00E4
 #define TC358768_DBG_DATA		0x00E8
@@ -537,9 +540,21 @@ static ssize_t tc358768_dsi_host_transfer(struct mipi_dsi_host *host,
 		return -ENOTSUPP;
 	}
 
+	if (msg->tx_len > 1024) {
+		dev_warn(priv->dev, "Maximum 1024 byte MIPI tx is supported\n");
+		return -EINVAL;
+	}
+
 	if (msg->tx_len > 8) {
-		dev_warn(priv->dev, "Maximum 8 byte MIPI tx is supported\n");
-		return -ENOTSUPP;
+		u32 confctl;
+
+		tc358768_read(priv, TC358768_CONFCTL, &confctl);
+
+		if (confctl & BIT(6)) {
+			dev_warn(priv->dev,
+				 "Video is currently active. Unable to transmit long command\n");
+			return -EBUSY;
+		}
 	}
 
 	ret = mipi_dsi_create_packet(&packet, msg);
@@ -552,23 +567,66 @@ static ssize_t tc358768_dsi_host_transfer(struct mipi_dsi_host *host,
 		tc358768_write(priv, TC358768_DSICMD_WC, 0);
 		tc358768_write(priv, TC358768_DSICMD_WD0,
 			       (packet.header[2] << 8) | packet.header[1]);
-	} else {
-		int i;
-
+		tc358768_dsicmd_tx(priv);
+	} else if (packet.payload_length <= 8) {
 		tc358768_write(priv, TC358768_DSICMD_TYPE,
 			       (0x40 << 8) | (packet.header[0] & 0x3f));
 		tc358768_write(priv, TC358768_DSICMD_WC, packet.payload_length);
-		for (i = 0; i < packet.payload_length; i += 2) {
+
+		for (int i = 0; i < packet.payload_length; i += 2) {
 			u16 val = packet.payload[i];
 
 			if (i + 1 < packet.payload_length)
 				val |= packet.payload[i + 1] << 8;
-
 			tc358768_write(priv, TC358768_DSICMD_WD0 + i, val);
 		}
-	}
 
-	tc358768_dsicmd_tx(priv);
+		tc358768_dsicmd_tx(priv);
+	} else {
+		unsigned long tx_sleep_us;
+		size_t len;
+
+		/* For packets over 8 bytes we need to use the video buffer */
+		tc358768_write(priv, TC358768_DATAFMT, BIT(0));	/* txdt_en */
+		tc358768_write(priv, TC358768_DSITX_DT, packet.header[0] & 0x3f);
+		tc358768_write(priv, TC358768_CMDBYTE, packet.payload_length);
+		tc358768_write(priv, TC358768_VBUFCTRL, TC358768_VBUFCTRL_VBUF_EN);
+
+		/*
+		 * Write the payload in 2-byte chunks, and pad with zeroes to
+		 * align to 4 bytes.
+		 */
+		len = ALIGN(packet.payload_length, 4);
+
+		for (int i = 0; i < len; i += 2) {
+			u16 val = 0;
+
+			if (i < packet.payload_length)
+				val |= packet.payload[i];
+			if (i + 1 < packet.payload_length)
+				val |= packet.payload[i + 1] << 8;
+
+			tc358768_write(priv, TC358768_DBG_DATA, val);
+		}
+
+		/* Start transmission */
+		tc358768_write(priv, TC358768_VBUFCTRL,
+			       TC358768_VBUFCTRL_VBUF_EN |
+			       TC358768_VBUFCTRL_TX_EN |
+			       TC358768_VBUFCTRL_MASK);
+
+		/*
+		 * The TC358768 spec says to wait until the transmission has
+		 * been finished, estimating the sleep time based on the payload
+		 * and clock rates. We use a simple safe estimate of 2us per
+		 * byte (LP mode transmission).
+		 */
+		tx_sleep_us = packet.payload_length * 2;
+		usleep_range(tx_sleep_us, tx_sleep_us * 2);
+
+		tc358768_write(priv, TC358768_VBUFCTRL, TC358768_VBUFCTRL_MASK);
+		tc358768_write(priv, TC358768_VBUFCTRL, 0); /* Stop transmission */
+	}
 
 	ret = tc358768_clear_error(priv);
 	if (ret)
@@ -752,6 +810,9 @@ static void tc358768_bridge_atomic_pre_enable(struct drm_bridge *bridge,
 		return;
 	}
 
+	/* Release RstPtr so that the video buffer can be used for DSI commands */
+	tc358768_update_bits(priv, TC358768_PP_MISC, BIT(14), 0);
+
 	connector = drm_atomic_get_new_connector_for_encoder(state, bridge->encoder);
 	conn_state = drm_atomic_get_new_connector_state(state, connector);
 	crtc_state = drm_atomic_get_new_crtc_state(state, conn_state->crtc);

-- 
2.43.0