Re: [PATCH v2 4/9] drm/panthor: Implement optional reset

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 21 Mar 2025 21:05:54 +0100
Marek Vasut <marex@denx.de> wrote:

> The instance of the GPU populated in Freescale i.MX95 does require
> release from reset by writing into a single GPUMIX block controller
> GPURESET register bit 0. Implement support for one optional reset.
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Boris Brezillon <boris.brezillon@collabora.com>
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Fabio Estevam <festevam@gmail.com>
> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> Cc: Liviu Dudau <liviu.dudau@arm.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
> Cc: Philipp Zabel <p.zabel@pengutronix.de>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Sascha Hauer <s.hauer@pengutronix.de>
> Cc: Sebastian Reichel <sre@kernel.org>
> Cc: Shawn Guo <shawnguo@kernel.org>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: devicetree@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: imx@lists.linux.dev
> Cc: linux-arm-kernel@lists.infradead.org
> ---
> V2: Drop the select RESET_SIMPLE from Kconfig
> ---
>  drivers/gpu/drm/panthor/panthor_device.c | 23 +++++++++++++++++++++++
>  drivers/gpu/drm/panthor/panthor_device.h |  3 +++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index a9da1d1eeb707..51ee9cae94504 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -64,6 +64,17 @@ static int panthor_clk_init(struct panthor_device *ptdev)
>  	return 0;
>  }
>  
> +static int panthor_reset_init(struct panthor_device *ptdev)
> +{
> +	ptdev->resets = devm_reset_control_get_optional_exclusive_deasserted(ptdev->base.dev, NULL);
> +	if (IS_ERR(ptdev->resets))
> +		return dev_err_probe(ptdev->base.dev,
> +				     PTR_ERR(ptdev->resets),
> +				     "get reset failed");
> +
> +	return 0;
> +}
> +
>  void panthor_device_unplug(struct panthor_device *ptdev)
>  {
>  	/* This function can be called from two different path: the reset work
> @@ -217,6 +228,10 @@ int panthor_device_init(struct panthor_device *ptdev)
>  	if (ret)
>  		return ret;
>  
> +	ret = panthor_reset_init(ptdev);
> +	if (ret)
> +		return ret;
> +
>  	ret = panthor_devfreq_init(ptdev);
>  	if (ret)
>  		return ret;
> @@ -470,6 +485,10 @@ int panthor_device_resume(struct device *dev)
>  	if (ret)
>  		goto err_disable_stacks_clk;
>  
> +	ret = reset_control_deassert(ptdev->resets);
> +	if (ret)
> +		goto err_disable_coregroup_clk;
> +
>  	panthor_devfreq_resume(ptdev);
>  
>  	if (panthor_device_is_initialized(ptdev) &&
> @@ -512,6 +531,9 @@ int panthor_device_resume(struct device *dev)
>  
>  err_suspend_devfreq:
>  	panthor_devfreq_suspend(ptdev);
> +	reset_control_assert(ptdev->resets);
> +
> +err_disable_coregroup_clk:
>  	clk_disable_unprepare(ptdev->clks.coregroup);
>  
>  err_disable_stacks_clk:
> @@ -563,6 +585,7 @@ int panthor_device_suspend(struct device *dev)
>  
>  	panthor_devfreq_suspend(ptdev);
>  
> +	reset_control_assert(ptdev->resets);

Hm, that might be the cause of the fast reset issue (which is a fast
resume more than a fast reset BTW): if you re-assert the reset line on
runtime suspend, I guess this causes a full GPU reset, and the MCU ends
up in a state where it needs a slow reset (all data sections reset to
their initial state). Can you try to move the reset_control_[de]assert
to the unplug/init functions?

>  	clk_disable_unprepare(ptdev->clks.coregroup);
>  	clk_disable_unprepare(ptdev->clks.stacks);
>  	clk_disable_unprepare(ptdev->clks.core);
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index da6574021664b..fea3a05778e2e 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -111,6 +111,9 @@ struct panthor_device {
>  		struct clk *coregroup;
>  	} clks;
>  
> +	/** @resets: GPU reset. */
> +	struct reset_control *resets;
> +
>  	/** @coherent: True if the CPU/GPU are memory coherent. */
>  	bool coherent;
>