linux-kernel - [PATCH] drm/stm: dsi: compute the transition time from LP to HS and back

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Date:   Tue, 13 Jul 2021 16:49:41 +0200
From:   Antonio Borneo <antonio.borneo@...s.st.com>
To:     Yannick Fertre <yannick.fertre@...s.st.com>,
        Philippe Cornu <philippe.cornu@...s.st.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     Antonio Borneo <antonio.borneo@...s.st.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] drm/stm: dsi: compute the transition time from LP to HS and back

The driver uses a conservative set of hardcoded values for the
maximum time delay of the transitions between LP and HS, either
for data and clock lanes.

By using the info in STM32MP157 datasheet, valid also for other ST
devices, compute the actual delay from the lane's bps.

Signed-off-by: Antonio Borneo <antonio.borneo@...s.st.com>
---
To: Yannick Fertre <yannick.fertre@...s.st.com>
To: Philippe Cornu <philippe.cornu@...s.st.com>
To: Benjamin Gaignard <benjamin.gaignard@...aro.org>
To: David Airlie <airlied@...ux.ie>
To: Daniel Vetter <daniel@...ll.ch>
To: Maxime Coquelin <mcoquelin.stm32@...il.com>
To: Alexandre Torgue <alexandre.torgue@...s.st.com>
To: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
To: dri-devel@...ts.freedesktop.org
To: linux-stm32@...md-mailman.stormreply.com
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org

 drivers/gpu/drm/stm/dw_mipi_dsi-stm.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
index 8399d337589d..32cb41b2202f 100644
--- a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
+++ b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
@@ -309,14 +309,23 @@ dw_mipi_dsi_get_lane_mbps(void *priv_data, const struct drm_display_mode *mode,
 	return 0;
 }
 
+#define DSI_PHY_DELAY(fp, vp, mbps) DIV_ROUND_UP((fp) * (mbps) + 1000 * (vp), 8000)
+
 static int
 dw_mipi_dsi_phy_get_timing(void *priv_data, unsigned int lane_mbps,
 			   struct dw_mipi_dsi_dphy_timing *timing)
 {
-	timing->clk_hs2lp = 0x40;
-	timing->clk_lp2hs = 0x40;
-	timing->data_hs2lp = 0x40;
-	timing->data_lp2hs = 0x40;
+	/*
+	 * From STM32MP157 datasheet, valid for STM32F469, STM32F7x9, STM32H747
+	 * phy_clkhs2lp_time = (272+136*UI)/(8*UI)
+	 * phy_clklp2hs_time = (512+40*UI)/(8*UI)
+	 * phy_hs2lp_time = (192+64*UI)/(8*UI)
+	 * phy_lp2hs_time = (256+32*UI)/(8*UI)
+	 */
+	timing->clk_hs2lp = DSI_PHY_DELAY(272, 136, lane_mbps);
+	timing->clk_lp2hs = DSI_PHY_DELAY(512, 40, lane_mbps);
+	timing->data_hs2lp = DSI_PHY_DELAY(192, 64, lane_mbps);
+	timing->data_lp2hs = DSI_PHY_DELAY(256, 32, lane_mbps);
 
 	return 0;
 }

base-commit: 35d283658a6196b2057be562096610c6793e1219
-- 
2.32.0