Re: [PATCH 1/3] drm/modeset: Prime modeset lock vs dma_resv

From: "Christian König" <christian.koenig@amd.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 1/3] drm/modeset: Prime modeset lock vs dma_resv
Date: Wed, 20 Nov 2019 09:34:03 +0100	[thread overview]
Message-ID: <9ce03b86-3bec-3a33-b5d0-4acbe9e861ec@amd.com> (raw)
In-Reply-To: <20191119210844.16947-2-daniel.vetter@ffwll.ch>

Am 19.11.19 um 22:08 schrieb Daniel Vetter:
> It's kinda really hard to get this wrong on a driver with both display
> and dma_resv locking. But who ever knows, so better to make sure that
> really all drivers nest these the same way.
>
> For actual lock semantics the acquire context nesting doesn't matter.
> But to teach lockdep what's going on with ww_mutex the acquire ctx is
> a fake lockdep lock, hence from a lockdep pov it does matter. That's
> why I figured better to include it.
>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Why not add another __init function like we did for dma_resv? That 
looked rather clean to me.

Either why feel free to add an Acked-by: Christian König 
<christian.koenig@amd.com> to the patch.

Regards,
Christian.

> ---
>   drivers/gpu/drm/drm_mode_config.c | 28 ++++++++++++++++++++++++++++
>   1 file changed, 28 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 3b570a404933..08e6eff6a179 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -27,6 +27,7 @@
>   #include <drm/drm_file.h>
>   #include <drm/drm_mode_config.h>
>   #include <drm/drm_print.h>
> +#include <linux/dma-resv.h>
>   
>   #include "drm_crtc_internal.h"
>   #include "drm_internal.h"
> @@ -415,6 +416,33 @@ void drm_mode_config_init(struct drm_device *dev)
>   	dev->mode_config.num_crtc = 0;
>   	dev->mode_config.num_encoder = 0;
>   	dev->mode_config.num_total_plane = 0;
> +
> +	if (IS_ENABLED(CONFIG_LOCKDEP)) {
> +		struct drm_modeset_acquire_ctx modeset_ctx;
> +		struct ww_acquire_ctx resv_ctx;
> +		struct dma_resv resv;
> +		int ret;
> +
> +		dma_resv_init(&resv);
> +
> +		drm_modeset_acquire_init(&modeset_ctx, 0);
> +		ret = drm_modeset_lock(&dev->mode_config.connection_mutex,
> +				       &modeset_ctx);
> +		if (ret == -EDEADLK)
> +			ret = drm_modeset_backoff(&modeset_ctx);
> +
> +		ww_acquire_init(&resv_ctx, &reservation_ww_class);
> +		ret = dma_resv_lock(&resv, &resv_ctx);
> +		if (ret == -EDEADLK)
> +			dma_resv_lock_slow(&resv, &resv_ctx);
> +
> +		dma_resv_unlock(&resv);
> +		ww_acquire_fini(&resv_ctx);
> +
> +		drm_modeset_drop_locks(&modeset_ctx);
> +		drm_modeset_acquire_fini(&modeset_ctx);
> +		dma_resv_fini(&resv);
> +	}
>   }
>   EXPORT_SYMBOL(drm_mode_config_init);
>   

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