linux-kernel - [PATCH v2] drm: bridge: icn6211: Adjust clock phase using SYS_CTRL

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Date:   Mon, 23 May 2022 23:01:44 +1000
From:   Jonathan Liu <net147@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Marek Vasut <marex@...x.de>, Maxime Ripard <maxime@...no.tech>,
        Jonathan Liu <net147@...il.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: [PATCH v2] drm: bridge: icn6211: Adjust clock phase using SYS_CTRL_1

The code from [1] sets SYS_CTRL_1 to different values depending on the
desired clock phase (0, 1/4, 1/2 or 3/4). A clock phase of 0 aligns the
positive edge of the clock with the pixel data while other values delay
the clock by a fraction of the clock period. A clock phase of 1/2 aligns
the negative edge of the clock with the pixel data.

The driver currently hard codes SYS_CTRL_1 to 0x88 which corresponds to
aligning the positive edge of the clock with the pixel data. This won't
work correctly for panels that require aligning the negative edge of the
clock with the pixel data.

Adjust the clock phase to 0 if DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE is
present in bus_flags, otherwise adjust the clock phase to 1/2 as
appropriate for DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE.

[1] https://github.com/tdjastrzebski/ICN6211-Configurator

Signed-off-by: Jonathan Liu <net147@...il.com>
---
V2: Use GENMASK and FIELD_PREP macros
---
 drivers/gpu/drm/bridge/chipone-icn6211.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/chipone-icn6211.c b/drivers/gpu/drm/bridge/chipone-icn6211.c
index 47dea657a752..f1538fb5f8a9 100644
--- a/drivers/gpu/drm/bridge/chipone-icn6211.c
+++ b/drivers/gpu/drm/bridge/chipone-icn6211.c
@@ -9,6 +9,8 @@
 #include <drm/drm_print.h>
 #include <drm/drm_mipi_dsi.h>
 
+#include <linux/bitfield.h>
+#include <linux/bits.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
@@ -26,6 +28,11 @@
 #define PD_CTRL(n)		(0x0a + ((n) & 0x3)) /* 0..3 */
 #define RST_CTRL(n)		(0x0e + ((n) & 0x1)) /* 0..1 */
 #define SYS_CTRL(n)		(0x10 + ((n) & 0x7)) /* 0..4 */
+#define SYS_CTRL_1_CLK_PHASE_MSK	GENMASK(5, 4)
+#define CLK_PHASE_0			0
+#define CLK_PHASE_1_4			1
+#define CLK_PHASE_1_2			2
+#define CLK_PHASE_3_4			3
 #define RGB_DRV(n)		(0x18 + ((n) & 0x3)) /* 0..3 */
 #define RGB_DLY(n)		(0x1c + ((n) & 0x1)) /* 0..1 */
 #define RGB_TEST_CTRL		0x1e
@@ -336,7 +343,7 @@ 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, id[4];
+	u8 pol, sys_ctrl_1, id[4];
 
 	chipone_readb(icn, VENDOR_ID, id);
 	chipone_readb(icn, DEVICE_ID_H, id + 1);
@@ -414,7 +421,14 @@ static void chipone_atomic_enable(struct drm_bridge *bridge,
 	chipone_configure_pll(icn, mode);
 
 	chipone_writeb(icn, SYS_CTRL(0), 0x40);
-	chipone_writeb(icn, SYS_CTRL(1), 0x88);
+	sys_ctrl_1 = 0x88;
+
+	if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE)
+		sys_ctrl_1 |= FIELD_PREP(SYS_CTRL_1_CLK_PHASE_MSK, CLK_PHASE_0);
+	else
+		sys_ctrl_1 |= FIELD_PREP(SYS_CTRL_1_CLK_PHASE_MSK, CLK_PHASE_1_2);
+
+	chipone_writeb(icn, SYS_CTRL(1), sys_ctrl_1);
 
 	/* icn6211 specific sequence */
 	chipone_writeb(icn, MIPI_FORCE_0, 0x20);
-- 
2.36.1