linux-kernel - [PATCH v2 5/5] fbdev/simplefb: Add support for interconnect paths

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Message-Id: <20250623-simple-drm-fb-icc-v2-5-f69b86cd3d7d@fairphone.com>
Date: Mon, 23 Jun 2025 08:44:49 +0200
From: Luca Weiss <luca.weiss@...rphone.com>
To: Hans de Goede <hdegoede@...hat.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Javier Martinez Canillas <javierm@...hat.com>, Helge Deller <deller@....de>
Cc: linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Luca Weiss <luca.weiss@...rphone.com>
Subject: [PATCH v2 5/5] fbdev/simplefb: Add support for interconnect paths

Some devices might require keeping an interconnect path alive so that
the framebuffer continues working. Add support for that by setting the
bandwidth requirements appropriately for all provided interconnect
paths.

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
---
 drivers/video/fbdev/simplefb.c | 83 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
index db27d51046af5cc3c46a0bc81ad9d9ed9a0783cc..b7e2f2374e3149866fd6f1803931e7f34dbbd75f 100644
--- a/drivers/video/fbdev/simplefb.c
+++ b/drivers/video/fbdev/simplefb.c
@@ -16,6 +16,7 @@
 #include <linux/clk.h>
 #include <linux/errno.h>
 #include <linux/fb.h>
+#include <linux/interconnect.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -89,6 +90,10 @@ struct simplefb_par {
 	u32 regulator_count;
 	struct regulator **regulators;
 #endif
+#if defined CONFIG_OF && defined CONFIG_INTERCONNECT
+	unsigned int icc_count;
+	struct icc_path **icc_paths;
+#endif
 };
 
 static void simplefb_clocks_destroy(struct simplefb_par *par);
@@ -525,6 +530,80 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
 }
 #endif
 
+#if defined CONFIG_OF && defined CONFIG_INTERCONNECT
+/*
+ * Generic interconnect path handling code.
+ */
+static void simplefb_detach_icc(void *res)
+{
+	struct simplefb_par *par = res;
+	int i;
+
+	for (i = par->icc_count - 1; i >= 0; i--) {
+		if (!IS_ERR_OR_NULL(par->icc_paths[i]))
+			icc_put(par->icc_paths[i]);
+	}
+}
+
+static int simplefb_attach_icc(struct simplefb_par *par,
+			       struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	int ret, count, i;
+
+	count = of_count_phandle_with_args(dev->of_node, "interconnects",
+							 "#interconnect-cells");
+	if (count < 0)
+		return 0;
+
+	/* An interconnect path consists of two elements */
+	if (count % 2) {
+		dev_err(dev, "invalid interconnects value\n");
+		return -EINVAL;
+	}
+	par->icc_count = count / 2;
+
+	par->icc_paths = devm_kcalloc(dev, par->icc_count,
+				      sizeof(*par->icc_paths),
+				      GFP_KERNEL);
+	if (!par->icc_paths)
+		return -ENOMEM;
+
+	for (i = 0; i < par->icc_count; i++) {
+		par->icc_paths[i] = of_icc_get_by_index(dev, i);
+		if (IS_ERR_OR_NULL(par->icc_paths[i])) {
+			ret = PTR_ERR(par->icc_paths[i]);
+			if (ret == -EPROBE_DEFER)
+				goto err;
+			dev_err(dev, "failed to get interconnect path %u: %d\n", i, ret);
+			continue;
+		}
+
+		ret = icc_set_bw(par->icc_paths[i], 0, UINT_MAX);
+		if (ret) {
+			dev_err(dev, "failed to set interconnect bandwidth %u: %d\n", i, ret);
+			continue;
+		}
+	}
+
+	return devm_add_action_or_reset(dev, simplefb_detach_icc, par);
+
+err:
+	while (i) {
+		--i;
+		if (!IS_ERR_OR_NULL(par->icc_paths[i]))
+			icc_put(par->icc_paths[i]);
+	}
+	return ret;
+}
+#else
+static int simplefb_attach_icc(struct simplefb_par *par,
+			       struct platform_device *pdev)
+{
+	return 0;
+}
+#endif
+
 static int simplefb_probe(struct platform_device *pdev)
 {
 	int ret;
@@ -615,6 +694,10 @@ static int simplefb_probe(struct platform_device *pdev)
 	if (ret < 0)
 		goto error_regulators;
 
+	ret = simplefb_attach_icc(par, pdev);
+	if (ret < 0)
+		goto error_regulators;
+
 	simplefb_clocks_enable(par, pdev);
 	simplefb_regulators_enable(par, pdev);
 

-- 
2.50.0