linux-kernel - Re: [PATCH v4 3/3] drm/panfrost: Synchronize and disable interrupts before powering off

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Message-ID: <b3855e51-6e44-402e-9727-d67ac6ae64b5@samsung.com>
Date:   Mon, 4 Dec 2023 17:05:33 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        boris.brezillon@...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, krzysztof.kozlowski@...aro.org
Subject: Re: [PATCH v4 3/3] drm/panfrost: Synchronize and disable interrupts
 before powering off

On 04.12.2023 12:42, AngeloGioacchino Del Regno 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 requires 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 an `is_suspended` bitmap which is used to address the
> possible corner case of unintentional IRQ unmasking because of ISR
> execution after a call to synchronize_irq().
>
> At resume, clear each is_suspended bit in the reset path of JOB/MMU
> to allow unmasking the interrupts.
>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>


Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>


> ---
>   drivers/gpu/drm/panfrost/panfrost_device.c |  3 +++
>   drivers/gpu/drm/panfrost/panfrost_device.h |  8 +++++++
>   drivers/gpu/drm/panfrost/panfrost_gpu.c    | 18 +++++++++++++--
>   drivers/gpu/drm/panfrost/panfrost_gpu.h    |  1 +
>   drivers/gpu/drm/panfrost/panfrost_job.c    | 26 ++++++++++++++++++----
>   drivers/gpu/drm/panfrost/panfrost_job.h    |  1 +
>   drivers/gpu/drm/panfrost/panfrost_mmu.c    | 22 +++++++++++++++---
>   drivers/gpu/drm/panfrost/panfrost_mmu.h    |  1 +
>   8 files changed, 71 insertions(+), 9 deletions(-)
>
> ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland