[RFC PATCH v2 10/19] drm/imagination: Add reset controller support for GPU initialization

[Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>]

Certain platforms, such as the T-Head TH1520 and Banana Pi BPI-F3,
require a controlled GPU reset sequence during the power-up procedure
to ensure proper initialization. Without this reset, the GPU may remain
in an undefined state, potentially leading to stability or performance
issues.

This commit integrates a dedicated reset controller within the
drm/imagination driver. By doing so, the driver can coordinate the
necessary reset operations as part of the normal GPU bring-up process,
improving reliability and ensuring that the hardware is ready for
operation.

Signed-off-by: Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>
---
 drivers/gpu/drm/imagination/pvr_device.c | 21 +++++++++++++++++++++
 drivers/gpu/drm/imagination/pvr_device.h |  9 +++++++++
 drivers/gpu/drm/imagination/pvr_power.c  | 15 ++++++++++++++-
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/imagination/pvr_device.c b/drivers/gpu/drm/imagination/pvr_device.c
index 1704c0268589..83a8ba70a30e 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, "gpu");
+	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
@@ -509,6 +525,11 @@ 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 6d0dfacb677b..f6576c08111c 100644
--- a/drivers/gpu/drm/imagination/pvr_device.h
+++ b/drivers/gpu/drm/imagination/pvr_device.h
@@ -131,6 +131,15 @@ struct pvr_device {
 	 */
 	struct clk *mem_clk;
 
+	/**
+	 * @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 ba7816fd28ec..87a955600d8b 100644
--- a/drivers/gpu/drm/imagination/pvr_power.c
+++ b/drivers/gpu/drm/imagination/pvr_power.c
@@ -15,6 +15,7 @@
 #include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 #include <linux/timer.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
@@ -252,6 +253,9 @@ pvr_power_device_suspend(struct device *dev)
 	clk_disable_unprepare(pvr_dev->sys_clk);
 	clk_disable_unprepare(pvr_dev->core_clk);
 
+	if (pvr_dev->reset)
+		err = reset_control_assert(pvr_dev->reset);
+
 err_drm_dev_exit:
 	drm_dev_exit(idx);
 
@@ -282,16 +286,25 @@ pvr_power_device_resume(struct device *dev)
 	if (err)
 		goto err_sys_clk_disable;
 
+	if (pvr_dev->reset) {
+		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);
 
-- 
2.34.1