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

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Date:	Fri, 23 May 2014 15:01:26 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Lucas Stach <l.stach@...gutronix.de>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	David Airlie <airlied@...ux.ie>,
	Ben Skeggs <bskeggs@...hat.com>, Lucas Stach <dev@...xeye.de>,
	Thierry Reding <thierry.reding@...il.com>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 3/4] drm/nouveau: hook up cache sync functions

On Mon, May 19, 2014 at 6:31 PM, Lucas Stach <l.stach@...gutronix.de> wrote:
> 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.

If Ben agrees with it I am also perfectly fine with getting rid of this #ifdef.
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