drm: bridge: icn6211: Read and validate chip IDs before configuration

Read out the Vendor/Chip/Version ID registers from the chip before
performing any configuration, and validate that the registers have
correct values. This is mostly a simple test whether DSI register
access does work, since that tends to be broken on various bridges.
Acked-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
To: dri-devel@lists.freedesktop.org
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331150509.9838-12-marex@denx.de

drivers/gpu/drm/bridge/chipone-icn6211.c

@@ -151,6 +151,14 @@ static inline struct chipone *bridge_to_chipone(struct drm_bridge *bridge)
 	return container_of(bridge, struct chipone, bridge);
 }
 
+static void chipone_readb(struct chipone *icn, u8 reg, u8 *val)
+{
+	if (icn->interface_i2c)
+		*val = i2c_smbus_read_byte_data(icn->client, reg);
+	else
+		mipi_dsi_generic_read(icn->dsi, (u8[]){reg, 1}, 2, val, 1);
+}
+
 static int chipone_writeb(struct chipone *icn, u8 reg, u8 val)
 {
 	if (icn->interface_i2c)
@@ -250,7 +258,21 @@ static void chipone_atomic_enable(struct drm_bridge *bridge,
 	const struct drm_bridge_state *bridge_state;
 	u16 hfp, hbp, hsync;
 	u32 bus_flags;
-	u8 pol;
+	u8 pol, id[4];
+
+	chipone_readb(icn, VENDOR_ID, id);
+	chipone_readb(icn, DEVICE_ID_H, id + 1);
+	chipone_readb(icn, DEVICE_ID_L, id + 2);
+	chipone_readb(icn, VERSION_ID, id + 3);
+
+	dev_dbg(icn->dev,
+		"Chip IDs: Vendor=0x%02x Device=0x%02x:0x%02x Version=0x%02x\n",
+		id[0], id[1], id[2], id[3]);
+
+	if (id[0] != 0xc1 || id[1] != 0x62 || id[2] != 0x11) {
+		dev_dbg(icn->dev, "Invalid Chip IDs, aborting configuration\n");
+		return;
+	}
 
 	/* Get the DPI flags from the bridge state. */
 	bridge_state = drm_atomic_get_new_bridge_state(state, bridge);