[PATCH v4 10/18] drm/imagination: Add reset controller support for GPU initialization

Michal Wilczynski
2025-01-28T19:48:41Z

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@samsung.com>
---
drivers/gpu/drm/imagination/pvr_device.c | 21 +++++++++++++++++++++
drivers/gpu/drm/imagination/pvr_device.h | 9 +++++++++
drivers/gpu/drm/imagination/pvr_power.c | 12 +++++++++++-
3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/imagination/pvr_device.c b/drivers/gpu/drm/imagination/pvr_device.c
index 1704c0268589..ef73e95157ee 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
@@ -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..e39460d594bd 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 +253,8 @@ 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);

@@ -282,16 +285,23 @@ pvr_power_device_resume(struct device *dev)
if (err)
goto err_sys_clk_disable;

+ 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