linux-kernel - Re: [PATCH v2 3/3] drm/panfrost: Synchronize and disable interrupts before powering off

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Message-ID: <20231128150612.17f6a095@collabora.com>
Date:   Tue, 28 Nov 2023 15:06:12 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     robh@...nel.org, steven.price@....com,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, m.szyprowski@...sung.com,
        krzysztof.kozlowski@...aro.org
Subject: Re: [PATCH v2 3/3] drm/panfrost: Synchronize and disable interrupts
 before powering off

On Tue, 28 Nov 2023 13:45:10 +0100
AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
wrote:

> To make sure that we don't unintentionally perform any unclocked and/or
> unpowered R/W operation on GPU registers, before turning off clocks and
> regulators we must make sure that no GPU, JOB or MMU ISR execution is
> pending: doing that required to add a mechanism to synchronize the
> interrupts on suspend.
> 
> Add functions panfrost_{gpu,job,mmu}_suspend_irq() which will perform
> interrupts masking and ISR execution synchronization, and then call
> those in the panfrost_device_runtime_suspend() handler in the exact
> sequence of job (may require mmu!) -> mmu -> gpu.
> 
> As a side note, JOB and MMU suspend_irq functions needed some special
> treatment: as their interrupt handlers will unmask interrupts, it was
> necessary to add a bitmap for "is_suspending" which is used to address
> the possible corner case of unintentional IRQ unmasking because of ISR
> execution after a call to synchronize_irq().
> 
> Of course, unmasking the interrupts is being done as part of the reset
> happening during runtime_resume(): since we're anyway resuming all of
> GPU, JOB, MMU, the only additional action is to zero out the newly
> introduced `is_suspending` bitmap directly in the resume handler, as
> to avoid adding panfrost_{job,mmu}_resume_irq() function just for
> clearing own bits, especially because it currently makes way more sense
> to just zero out the bitmap.
> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_device.c |  4 ++++
>  drivers/gpu/drm/panfrost/panfrost_device.h |  7 +++++++
>  drivers/gpu/drm/panfrost/panfrost_gpu.c    |  7 +++++++
>  drivers/gpu/drm/panfrost/panfrost_gpu.h    |  1 +
>  drivers/gpu/drm/panfrost/panfrost_job.c    | 18 +++++++++++++++---
>  drivers/gpu/drm/panfrost/panfrost_job.h    |  1 +
>  drivers/gpu/drm/panfrost/panfrost_mmu.c    | 17 ++++++++++++++---
>  drivers/gpu/drm/panfrost/panfrost_mmu.h    |  1 +
>  8 files changed, 50 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index c90ad5ee34e7..ed34aa55a7da 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -407,6 +407,7 @@ static int panfrost_device_runtime_resume(struct device *dev)
>  {
>  	struct panfrost_device *pfdev = dev_get_drvdata(dev);
>  
> +	bitmap_zero(pfdev->is_suspending, PANFROST_COMP_BIT_MAX);

I would let each sub-block clear their bit in the reset path, since
that's where the IRQs are effectively unmasked.

>  	panfrost_device_reset(pfdev);
>  	panfrost_devfreq_resume(pfdev);
>  
> @@ -421,6 +422,9 @@ static int panfrost_device_runtime_suspend(struct device *dev)
>  		return -EBUSY;
>  
>  	panfrost_devfreq_suspend(pfdev);
> +	panfrost_job_suspend_irq(pfdev);
> +	panfrost_mmu_suspend_irq(pfdev);
> +	panfrost_gpu_suspend_irq(pfdev);
>  	panfrost_gpu_power_off(pfdev);
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index 54a8aad54259..29f89f2d3679 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -25,6 +25,12 @@ struct panfrost_perfcnt;
>  #define NUM_JOB_SLOTS 3
>  #define MAX_PM_DOMAINS 5
>  
> +enum panfrost_drv_comp_bits {
> +	PANFROST_COMP_BIT_MMU,
> +	PANFROST_COMP_BIT_JOB,
> +	PANFROST_COMP_BIT_MAX
> +};
> +
>  /**
>   * enum panfrost_gpu_pm - Supported kernel power management features
>   * @GPU_PM_CLK_DIS:  Allow disabling clocks during system suspend
> @@ -109,6 +115,7 @@ struct panfrost_device {
>  
>  	struct panfrost_features features;
>  	const struct panfrost_compatible *comp;
> +	DECLARE_BITMAP(is_suspending, PANFROST_COMP_BIT_MAX);

nit: Maybe s/is_suspending/suspended_irqs/, given the state remains
until the device is resumed.