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Date: Thu, 23 Nov 2023 14:13:08 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>
Cc: steven.price@....com, robh@...nel.org,
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,
krzysztof.kozlowski@...aro.org
Subject: Re: [PATCH v3] drm/panfrost: Ignore core_mask for poweroff and sync
interrupts
On Thu, 23 Nov 2023 13:05:21 +0100
AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
wrote:
> Some SoCs may be equipped with a GPU containing two core groups
> and this is exactly the case of Samsung's Exynos 5422 featuring
> an ARM Mali-T628 MP6 GPU: the support for this GPU in Panfrost
> is partial, as this driver currently supports using only one
> core group and that's reflected on all parts of it, including
> the power on (and power off, previously to this patch) function.
>
> The issue with this is that even though executing the soft reset
> operation should power off all cores unconditionally, on at least
> one platform we're seeing a crash that seems to be happening due
> to an interrupt firing which may be because we are calling power
> transition only on the first core group, leaving the second one
> unchanged, or because ISR execution was pending before entering
> the panfrost_gpu_power_off() function and executed after powering
> off the GPU cores, or all of the above.
>
> Finally, solve this by introducing a new panfrost_gpu_suspend_irq()
> helper function and changing the panfrost_device_suspend() flow to
> 1. Mask and clear all interrupts: we don't need nor want any, as
> for power_off() we are polling PWRTRANS, but we anyway don't
> want GPU IRQs to fire while it is suspended/powered off;
> 2. Call synchronize_irq() after that to make sure that any pending
> ISR is executed before powering off the GPU Shaders/Tilers/L2
> hence avoiding unpowered registers R/W; and
> 3. Ignore the core_mask and ask the GPU to poweroff both core groups
>
> Of course it was also necessary to add a `irq` variable to `struct
> panfrost_device` as we need to get that in panfrost_gpu_power_off()
> for calling synchronize_irq() on it.
>
> Fixes: 22aa1a209018 ("drm/panfrost: Really power off GPU cores in panfrost_gpu_power_off()")
> [Regression detected on Odroid HC1, Exynos5422, Mali-T628 MP6]
> Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>
> Changes in v3:
> - Fix compile issue
>
> Changes in v2:
> - Fixed the commit hash of "Really power off [...]"
> - Actually based on a clean next-20231121
> - Renamed "irq" to "gpu_irq" as per Boris' suggestion
> - Moved the IRQ mask/clear/sync to a helper function and added
> a call to that in panfrost_device.c instead of doing that in
> panfrost_gpu_power_off().
>
> NOTE: I didn't split 1+2 from 3 as suggested by Boris, and I'm sending
> this one without waiting for feedback on my reasons for that which I
> explained as a reply to v1 because the former couldn't be applied to
> linux-next, and I want to unblock Krzysztof ASAP to get this tested.
>
> drivers/gpu/drm/panfrost/panfrost_device.c | 1 +
> drivers/gpu/drm/panfrost/panfrost_device.h | 1 +
> drivers/gpu/drm/panfrost/panfrost_gpu.c | 28 +++++++++++++++-------
> drivers/gpu/drm/panfrost/panfrost_gpu.h | 1 +
> 4 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index c90ad5ee34e7..b0a4f3e513f4 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -421,6 +421,7 @@ static int panfrost_device_runtime_suspend(struct device *dev)
> return -EBUSY;
>
> panfrost_devfreq_suspend(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 0fc558db6bfd..f2b1d4afb9e9 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -94,6 +94,7 @@ struct panfrost_device {
> struct device *dev;
> struct drm_device *ddev;
> struct platform_device *pdev;
> + int gpu_irq;
>
> void __iomem *iomem;
> struct clk *clock;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> index 09f5e1563ebd..2c09aede0945 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
> @@ -425,11 +425,10 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
>
> void panfrost_gpu_power_off(struct panfrost_device *pfdev)
> {
> - u64 core_mask = panfrost_get_core_mask(pfdev);
> int ret;
> u32 val;
>
> - gpu_write(pfdev, SHADER_PWROFF_LO, pfdev->features.shader_present & core_mask);
> + gpu_write(pfdev, SHADER_PWROFF_LO, pfdev->features.shader_present);
> ret = readl_relaxed_poll_timeout(pfdev->iomem + SHADER_PWRTRANS_LO,
> val, !val, 1, 1000);
> if (ret)
> @@ -441,16 +440,29 @@ void panfrost_gpu_power_off(struct panfrost_device *pfdev)
> if (ret)
> dev_err(pfdev->dev, "tiler power transition timeout");
>
> - gpu_write(pfdev, L2_PWROFF_LO, pfdev->features.l2_present & core_mask);
> + gpu_write(pfdev, L2_PWROFF_LO, pfdev->features.l2_present);
> ret = readl_poll_timeout(pfdev->iomem + L2_PWRTRANS_LO,
> val, !val, 0, 1000);
> if (ret)
> dev_err(pfdev->dev, "l2 power transition timeout");
> }
>
> +void panfrost_gpu_suspend_irq(struct panfrost_device *pfdev)
> +{
> + /* Disable all interrupts before suspending the GPU */
> + gpu_write(pfdev, GPU_INT_MASK, 0);
> + gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_MASK_ALL);
> +
> + /*
> + * Make sure that we don't have pending ISRs, otherwise we'll be
> + * reading and/or writing registers while the GPU is powered off
I see this comment, plus the fact you call panfrost_gpu_suspend_irq()
before panfrost_gpu_power_off() and I realize there might still be a
misunderstanding. It's not the l2,shader,tiler-poweroff that causes the
invalid reg access, it's what happens in the PM core after we've
returned from panfrost_device_runtime_suspend() (power domain turned
off). The register bank is still accessible when the sub-blocks are off,
otherwise we wouldn't be able to power them on after a reset (which
automatically powers off all the blocks, IIRC).
> + */
> + synchronize_irq(pfdev->gpu_irq);
> +}
> +
> int panfrost_gpu_init(struct panfrost_device *pfdev)
> {
> - int err, irq;
> + int err;
>
> err = panfrost_gpu_soft_reset(pfdev);
> if (err)
> @@ -465,11 +477,11 @@ int panfrost_gpu_init(struct panfrost_device *pfdev)
>
> dma_set_max_seg_size(pfdev->dev, UINT_MAX);
>
> - irq = platform_get_irq_byname(to_platform_device(pfdev->dev), "gpu");
> - if (irq < 0)
> - return irq;
> + pfdev->gpu_irq = platform_get_irq_byname(to_platform_device(pfdev->dev), "gpu");
> + if (pfdev->gpu_irq < 0)
> + return pfdev->gpu_irq;
>
> - err = devm_request_irq(pfdev->dev, irq, panfrost_gpu_irq_handler,
> + err = devm_request_irq(pfdev->dev, pfdev->gpu_irq, panfrost_gpu_irq_handler,
> IRQF_SHARED, KBUILD_MODNAME "-gpu", pfdev);
> if (err) {
> dev_err(pfdev->dev, "failed to request gpu irq");
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.h b/drivers/gpu/drm/panfrost/panfrost_gpu.h
> index 876fdad9f721..d841b86504ea 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.h
> @@ -15,6 +15,7 @@ u32 panfrost_gpu_get_latest_flush_id(struct panfrost_device *pfdev);
> int panfrost_gpu_soft_reset(struct panfrost_device *pfdev);
> void panfrost_gpu_power_on(struct panfrost_device *pfdev);
> void panfrost_gpu_power_off(struct panfrost_device *pfdev);
> +void panfrost_gpu_suspend_irq(struct panfrost_device *pfdev);
>
> void panfrost_cycle_counter_get(struct panfrost_device *pfdev);
> void panfrost_cycle_counter_put(struct panfrost_device *pfdev);
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