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

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Date:	Mon, 19 May 2014 10:46:21 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	David Airlie <airlied@...ux.ie>, Ben Skeggs <bskeggs@...hat.com>,
	Lucas Stach <dev@...xeye.de>, nouveau@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, gnurou@...il.com
Subject: Re: [PATCH 3/4] drm/nouveau: hook up cache sync functions

On Mon, May 19, 2014 at 04:10:57PM +0900, Alexandre Courbot wrote:
> 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>

Perhaps having a propery commit message here would be good.

> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
[...]
> +#ifdef NOUVEAU_NEED_CACHE_SYNC
> +void
> +nouveau_bo_sync_for_cpu(struct nouveau_bo *nvbo)
> +{
> +	struct nouveau_device *device;
> +	struct ttm_tt *ttm = nvbo->bo.ttm;
> +
> +	device = nouveau_dev(nouveau_bdev(ttm->bdev)->dev);
> +
> +	if (nvbo->bo.ttm && nvbo->bo.ttm->caching_state == tt_cached)
> +		ttm_dma_tt_cache_sync_for_cpu((struct ttm_dma_tt *)nvbo->bo.ttm,
> +					      nv_device_base(device));

Can we be certain at this point that the struct ttm_tt is in fact a
struct ttm_dma_tt?

> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.h b/drivers/gpu/drm/nouveau/nouveau_bo.h
[...]
> +#if IS_ENABLED(CONFIG_ARCH_TEGRA)
> +#define NOUVEAU_NEED_CACHE_SYNC
> +#endif

I know I gave this as an example myself when we discussed this offline,
but I'm now thinking that this might actually be better off in Kconfig.

> +#ifdef NOUVEAU_NEED_CACHE_SYNC
> +void nouveau_bo_sync_for_cpu(struct nouveau_bo *);
> +void nouveau_bo_sync_for_device(struct nouveau_bo *);
> +#else
> +static inline void
> +nouveau_bo_sync_for_cpu(struct nouveau_bo *)
> +{
> +}
> +
> +static inline void
> +nouveau_bo_sync_for_device(struct nouveau_bo *)
> +{
> +}
> +#endif
> +
> +

There's a gratuituous blank line here.

> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
> index c90c0dc0afe8..b7e42fdc9634 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> @@ -897,7 +897,13 @@ nouveau_gem_ioctl_cpu_prep(struct drm_device *dev, void *data,
>  	ret = ttm_bo_wait(&nvbo->bo, true, true, no_wait);
>  	spin_unlock(&nvbo->bo.bdev->fence_lock);
>  	drm_gem_object_unreference_unlocked(gem);
> -	return ret;
> +
> +	if (ret)
> +		return ret;
> +
> +	nouveau_bo_sync_for_cpu(nvbo);
> +
> +	return 0;
>  }

This could be rewritten as:

	if (!ret)
		nouveau_bo_sync_for_cpu(nvbo);

	return ret;

Which would be slightly shorter.

On second thought, perhaps part of nouveau_gem_ioctl_cpu_prep() could be
refactored into a separate function to make this more symmetric. If we
put that in nouveau_bo.c and name it nouveau_bo_wait() for example, the
dummies can go away and both nouveau_bo_sync_for_{cpu,device}() can be
made static. I also think that's cleaner because it has both variants of
the nouveau_bo_sync_for_*() calls in the same file.

Thierry

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