linux-kernel - Re: [PATCH 3/4] drm/nouveau: hook up cache sync functions

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Date:	Mon, 19 May 2014 11:31:27 +0200
From:	Lucas Stach <l.stach@...gutronix.de>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	David Airlie <airlied@...ux.ie>, Ben Skeggs <bskeggs@...hat.com>,
	Lucas Stach <dev@...xeye.de>,
	Thierry Reding <thierry.reding@...il.com>, gnurou@...il.com,
	nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 3/4] drm/nouveau: hook up cache sync functions

Am Montag, den 19.05.2014, 16:10 +0900 schrieb Alexandre Courbot:
> From: Lucas Stach <dev@...xeye.de>
> 
> Signed-off-by: Lucas Stach <dev@...xeye.de>
> [acourbot@...dia.com: make conditional and platform-friendly]
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_bo.c  | 32 ++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/nouveau/nouveau_bo.h  | 20 ++++++++++++++++++++
>  drivers/gpu/drm/nouveau/nouveau_gem.c |  8 +++++++-
>  3 files changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index b6dc85c614be..0886f47e5244 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -407,6 +407,8 @@ nouveau_bo_validate(struct nouveau_bo *nvbo, bool interruptible,
>  {
>  	int ret;
>  
> +	nouveau_bo_sync_for_device(nvbo);
> +
>  	ret = ttm_bo_validate(&nvbo->bo, &nvbo->placement,
>  			      interruptible, no_wait_gpu);
>  	if (ret)
> @@ -487,6 +489,36 @@ nouveau_bo_invalidate_caches(struct ttm_bo_device *bdev, uint32_t flags)
>  	return 0;
>  }
>  
> +#ifdef NOUVEAU_NEED_CACHE_SYNC

I don't like this ifdef at all. I know calling this functions will add a
little overhead to x86 where it isn't strictly required, but I think
it's negligible.

When I looked at them the dma_sync_single_for_[device|cpu] functions
which are called here map out to just a drain of the PCI store buffer on
x86, which should be fast enough to be done unconditionally. They won't
so any time-consuming cache synchronization on PCI coherent arches.

Regards,
Lucas

-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

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