On Mo, 2025-01-20 at 18:21 +0100, Michal Wilczynski wrote:
> 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.wilczyn...@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 | 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..7ae9875d8d74 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_exclusive_by_index(drm_dev->dev, 0);
The dt-bindings only specify a single reset. No need to request by
index. Please use:
reset = devm_reset_control_get_exclusive(drm_dev->dev, NULL);
instead. Or devm_reset_control_get_optional_exclusive(), perhaps? See
below.
> + 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 looks like the reset control really should be made optional in
pvr_device_reset_init().
> + *
> + * 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);
No need for conditional assert, reset_control_assert(NULL) is a no-op.
Just use:
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;
> + }
Same as above, reset_control_deassert(NULL) returns 0:
err = reset_control_deassert(pvr_dev->reset);
if (err)
goto err_mem_clk_disable;
regards
Philipp
