drm/imagination: Add reset controller support for GPU initialization

All IMG Rogue GPUs include a reset line that participates in the
power-up sequence. On some SoCs (e.g., T-Head TH1520 and Banana Pi
BPI-F3), this reset line is exposed and must be driven explicitly to
ensure proper initialization.  On others, such as the currently
supported TI SoC, the reset logic is handled in hardware or firmware
without exposing the line directly. In platforms where the reset line is
externally accessible, if it is not driven correctly, the GPU may remain
in an undefined state, leading to instability or performance issues.

This commit adds a dedicated reset controller to the drm/imagination
driver.  By managing the reset line (where applicable) as part of normal
GPU bring-up, the driver ensures reliable initialization across
platforms regardless of whether the reset is controlled externally or
handled internally.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Link: https://lore.kernel.org/r/20250418-apr_18_reset_img-v6-2-85a06757b698@samsung.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>

3 files changed, 51 insertions, 1 deletions

diff --git a/drivers/gpu/drm/imagination/pvr_device.c b/drivers/gpu/drm/imagination/pvr_device.c
index 1e488a30c784..8b9ba4983c4c 100644
--- a/drivers/gpu/drm/imagination/pvr_device.c
+++ b/drivers/gpu/drm/imagination/pvr_device.c
@@ -25,6 +25,7 @@
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 #include <linux/stddef.h>
 #include <linux/types.h>
@@ -120,6 +121,21 @@ static int pvr_device_clk_init(struct pvr_device *pvr_dev)
 	return 0;
 }
 
+static int pvr_device_reset_init(struct pvr_device *pvr_dev)
+{
+	struct drm_device *drm_dev = from_pvr_device(pvr_dev);
+	struct reset_control *reset;
+
+	reset = devm_reset_control_get_optional_exclusive(drm_dev->dev, NULL);
+	if (IS_ERR(reset))
+		return dev_err_probe(drm_dev->dev, PTR_ERR(reset),
+				     "failed to get gpu reset line\n");
+
+	pvr_dev->reset = reset;
+
+	return 0;
+}
+
 /**
  * pvr_device_process_active_queues() - Process all queue related events.
  * @pvr_dev: PowerVR device to check
@@ -615,6 +631,11 @@ pvr_device_init(struct pvr_device *pvr_dev)
 	if (err)
 		return err;
 
+	/* Get the reset line for the GPU */
+	err = pvr_device_reset_init(pvr_dev);
+	if (err)
+		return err;
+
 	/* Explicitly power the GPU so we can access control registers before the FW is booted. */
 	err = pm_runtime_resume_and_get(dev);
 	if (err)
diff --git a/drivers/gpu/drm/imagination/pvr_device.h b/drivers/gpu/drm/imagination/pvr_device.h
index eb5da8c7040f..7cb01c38d2a9 100644
--- a/drivers/gpu/drm/imagination/pvr_device.h
+++ b/drivers/gpu/drm/imagination/pvr_device.h
@@ -139,6 +139,15 @@ struct pvr_device {
 		u32 domain_count;
 	} power;
 
+	/**
+	 * @reset: Optional reset line.
+	 *
+	 * This may be used on some platforms to provide a reset line that needs to be de-asserted
+	 * after power-up procedure. It would also need to be asserted after the power-down
+	 * procedure.
+	 */
+	struct reset_control *reset;
+
 	/** @irq: IRQ number. */
 	int irq;
 
diff --git a/drivers/gpu/drm/imagination/pvr_power.c b/drivers/gpu/drm/imagination/pvr_power.c
index 19b079b357df..41f5d89e78b8 100644
--- a/drivers/gpu/drm/imagination/pvr_power.c
+++ b/drivers/gpu/drm/imagination/pvr_power.c
@@ -18,6 +18,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_domain.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 #include <linux/timer.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
@@ -255,6 +256,8 @@ pvr_power_device_suspend(struct device *dev)
 	clk_disable_unprepare(pvr_dev->sys_clk);
 	clk_disable_unprepare(pvr_dev->core_clk);
 
+	err = reset_control_assert(pvr_dev->reset);
+
 err_drm_dev_exit:
 	drm_dev_exit(idx);
 
@@ -285,16 +288,33 @@ pvr_power_device_resume(struct device *dev)
 	if (err)
 		goto err_sys_clk_disable;
 
+	/*
+	 * According to the hardware manual, a delay of at least 32 clock
+	 * cycles is required between de-asserting the clkgen reset and
+	 * de-asserting the GPU reset. Assuming a worst-case scenario with
+	 * a very high GPU clock frequency, a delay of 1 microsecond is
+	 * sufficient to ensure this requirement is met across all
+	 * feasible GPU clock speeds.
+	 */
+	udelay(1);
+
+	err = reset_control_deassert(pvr_dev->reset);
+	if (err)
+		goto err_mem_clk_disable;
+
 	if (pvr_dev->fw_dev.booted) {
 		err = pvr_power_fw_enable(pvr_dev);
 		if (err)
-			goto err_mem_clk_disable;
+			goto err_reset_assert;
 	}
 
 	drm_dev_exit(idx);
 
 	return 0;
 
+err_reset_assert:
+	reset_control_assert(pvr_dev->reset);
+
 err_mem_clk_disable:
 	clk_disable_unprepare(pvr_dev->mem_clk);