[PATCH v3] 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>
---
ChangeLov v2->v3:
- Fix up the HS speed to 275 MHz, as the speed is double
  data rate.
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 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
index 3ad4a46c4e94..8c00193c2400 100644
--- a/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
+++ b/drivers/gpu/drm/panel/panel-ilitek-ili9881c.c
@@ -465,6 +465,21 @@ 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 per lane for RGB888. As this is 4 bits at
+	 * the time, at double data rate the maximum HS frequency should
+	 * be:
+	 * 550/4 * 2 = 275 MHz.
+	 */
+	dsi->hs_rate = 275000000;
+	/*
+	 * 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