linux-kernel - [PATCH 2/6] drm/bridge: allow to specify data-enable polarity

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Date:   Tue,  4 Sep 2018 22:21:09 -0700
From:   Stefan Agner <stefan@...er.ch>
To:     linus.walleij@...aro.org, 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,
        Laurent.pinchart@...asonboard.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 2/6] drm/bridge: allow to specify data-enable polarity

Support boards with a passive RGB to VGA bridge which require a low
active data-enable polarity.

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
Alternatively a new dt binding could be introduced for dumb VGA bridges
requiring low active data enable... However, also other polarities might
need a specific polarity, hence this generic approach might be better.

 drivers/gpu/drm/bridge/dumb-vga-dac.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/dumb-vga-dac.c b/drivers/gpu/drm/bridge/dumb-vga-dac.c
index 7a5c24967115..2b8c3d629f2f 100644
--- a/drivers/gpu/drm/bridge/dumb-vga-dac.c
+++ b/drivers/gpu/drm/bridge/dumb-vga-dac.c
@@ -179,6 +179,7 @@ static struct i2c_adapter *dumb_vga_retrieve_ddc(struct device *dev)
 static int dumb_vga_probe(struct platform_device *pdev)
 {
 	struct dumb_vga *vga;
+	u32 de;
 
 	vga = devm_kzalloc(&pdev->dev, sizeof(*vga), GFP_KERNEL);
 	if (!vga)
@@ -194,6 +195,23 @@ static int dumb_vga_probe(struct platform_device *pdev)
 		dev_dbg(&pdev->dev, "No vdd regulator found: %d\n", ret);
 	}
 
+	vga->bridge.funcs = &dumb_vga_bridge_funcs;
+	vga->bridge.of_node = pdev->dev.of_node;
+	vga->bridge.timings = of_device_get_match_data(&pdev->dev);
+
+	if (!vga->bridge.timings &&
+	    !of_property_read_u32(pdev->dev.of_node, "de-active", &de)) {
+		struct drm_bridge_timings *timings;
+
+		timings = devm_kzalloc(&pdev->dev, sizeof(*timings), GFP_KERNEL);
+		if (!timings)
+			return -ENOMEM;
+
+		timings->bus_flags = de ? DRM_BUS_FLAG_DE_HIGH :
+					DRM_BUS_FLAG_DE_LOW;
+		vga->bridge.timings = timings;
+	}
+
 	vga->ddc = dumb_vga_retrieve_ddc(&pdev->dev);
 	if (IS_ERR(vga->ddc)) {
 		if (PTR_ERR(vga->ddc) == -ENODEV) {
@@ -205,10 +223,6 @@ static int dumb_vga_probe(struct platform_device *pdev)
 		}
 	}
 
-	vga->bridge.funcs = &dumb_vga_bridge_funcs;
-	vga->bridge.of_node = pdev->dev.of_node;
-	vga->bridge.timings = of_device_get_match_data(&pdev->dev);
-
 	drm_bridge_add(&vga->bridge);
 
 	return 0;
-- 
2.18.0