[PATCH v2] drm/panel: Set max rate for Ilitek ILI9881C

[Linus Walleij]

After adding the hs_rate and lp_rate fields to the DSI device
we need to populate these accordingly so display drivers can
respect them.

This figure for HS rate comes from the ILI9881C manual, the
calculation is explained in the comment.

Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Andrzej Hajda <a.hajda at samsung.com>
Acked-by: Maxime Ripard <maxime.ripard at bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
ChangeLog v1->v2:
- Add LP speed after Andrzej's observation.
- Collect Maxime's ACK (hope it's fine also with the LP speed)
---
 drivers/gpu/drm/panel/panel-ilitek-ili9881c.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
index 3ad4a46c4e94..bd276c666318 100644
--- a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
+++ b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
@@ -465,6 +465,19 @@ static int ili9881c_dsi_probe(struct mipi_dsi_device *dsi)
 	dsi->mode_flags = MIPI_DSI_MODE_VIDEO_SYNC_PULSE;
 	dsi->format = MIPI_DSI_FMT_RGB888;
 	dsi->lanes = 4;
+	/*
+	 * The datasheet (table 39) specifies "limited clock channel speed"
+	 * for 4 lanes as 550 Mbps for RGB888. As this is 4 bits at the time,
+	 * the maximum HS frequency is 550/4 = 137.5 MHz.
+	 */
+	dsi->hs_rate = 137500000;
+	/*
+	 * Table 42 says: "Length of LP-00, LP-01, LP-10 or LP-11 periods":
+	 * min 50ns, max 75ns. 1/50ns = max LPM rate = 20.000.000Hz.
+	 * Since LP transmissions are to periods per bit, this should be
+	 * 10 MHz.
+	 */
+	dsi->lp_rate = 10000000;
 
 	return mipi_dsi_attach(dsi);
 }
-- 
2.19.1