linux-kernel - [PATCH v2 3/8] drm/bridge: simplify bridge timing info

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Date:   Wed, 12 Sep 2018 11:32:17 -0700
From:   Stefan Agner <stefan@...er.ch>
To:     linus.walleij@...aro.org, Laurent.pinchart@...asonboard.com,
        airlied@...ux.ie, robh+dt@...nel.org, mark.rutland@....com,
        shawnguo@...nel.org, s.hauer@...gutronix.de, p.zabel@...gutronix.de
Cc:     kernel@...gutronix.de, fabio.estevam@....com, linux-imx@....com,
        architt@...eaurora.org, a.hajda@...sung.com, gustavo@...ovan.org,
        maarten.lankhorst@...ux.intel.com, sean@...rly.run,
        marcel.ziswiler@...adex.com, max.krummenacher@...adex.com,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Stefan Agner <stefan@...er.ch>
Subject: [PATCH v2 3/8] drm/bridge: simplify bridge timing info

Bridges are typically connected to a parallel display signal with
pixel clock, sync signals and data lines. Parallel display signals
are also used in lower-end embedded display panels. For parallel
display panels we currently do not specify setup/hold times. From
discussions on the mailing list it seems not convincing that this
is currently really required for bridges either.

Remove setup/hold timings again to better align timing information
of displays and briges.

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
 drivers/gpu/drm/bridge/dumb-vga-dac.c | 17 +++++------------
 include/drm/drm_bridge.h              | 14 --------------
 2 files changed, 5 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/bridge/dumb-vga-dac.c b/drivers/gpu/drm/bridge/dumb-vga-dac.c
index d5aa0f931ef2..b2309ad228cf 100644
--- a/drivers/gpu/drm/bridge/dumb-vga-dac.c
+++ b/drivers/gpu/drm/bridge/dumb-vga-dac.c
@@ -229,14 +229,14 @@ static int dumb_vga_remove(struct platform_device *pdev)
 /*
  * We assume the ADV7123 DAC is the "default" for historical reasons
  * Information taken from the ADV7123 datasheet, revision D.
- * NOTE: the ADV7123EP seems to have other timings and need a new timings
- * set if used.
  */
 static const struct drm_bridge_timings default_dac_timings = {
-	/* Timing specifications, datasheet page 7 */
+	/*
+	 * From Timing diagram, datasheet page 7. The bridge samples
+	 * on pixel clocks positive edge, hence the display controller
+	 * should drive signals on the negative edge.
+	 */
 	.input_bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE,
-	.setup_time_ps = 500,
-	.hold_time_ps = 1500,
 };
 
 /*
@@ -246,10 +246,6 @@ static const struct drm_bridge_timings default_dac_timings = {
 static const struct drm_bridge_timings ti_ths8134_dac_timings = {
 	/* From timing diagram, datasheet page 9 */
 	.input_bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE,
-	/* From datasheet, page 12 */
-	.setup_time_ps = 3000,
-	/* I guess this means latched input */
-	.hold_time_ps = 0,
 };
 
 /*
@@ -259,9 +255,6 @@ static const struct drm_bridge_timings ti_ths8134_dac_timings = {
 static const struct drm_bridge_timings ti_ths8135_dac_timings = {
 	/* From timing diagram, datasheet page 14 */
 	.input_bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE,
-	/* From datasheet, page 16 */
-	.setup_time_ps = 2000,
-	.hold_time_ps = 500,
 };
 
 static const struct of_device_id dumb_vga_match[] = {
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 45e90f4b46c3..1a1d08350eaf 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -251,20 +251,6 @@ struct drm_bridge_timings {
 	 * &drm_display_info->bus_flags.
 	 */
 	u32 input_bus_flags;
-	/**
-	 * @setup_time_ps:
-	 *
-	 * Defines the time in picoseconds the input data lines must be
-	 * stable before the clock edge.
-	 */
-	u32 setup_time_ps;
-	/**
-	 * @hold_time_ps:
-	 *
-	 * Defines the time in picoseconds taken for the bridge to sample the
-	 * input signal after the clock edge.
-	 */
-	u32 hold_time_ps;
 };
 
 /**
-- 
2.18.0