linux-kernel - Re: [PATCH] nouveau: fix nv40_perfctr

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Message-ID: <56E8E73C.5080400@redhat.com>
Date:	Wed, 16 Mar 2016 14:55:24 +1000
From:	Ben Skeggs <bskeggs@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>, David Airlie <airlied@...ux.ie>
Cc:	Samuel Pitoiset <samuel.pitoiset@...il.com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nouveau: fix nv40_perfctr_next() cleanup regression

On 03/15/2016 12:24 AM, Arnd Bergmann wrote:
> gcc-6 warns about code in the nouveau driver that is obviously silly:
> 
> drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c: In function 'nv40_perfctr_next':
> drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c:62:19: warning: self-comparison always evaluats to false [-Wtautological-compare]
>   if (pm->sequence != pm->sequence) {
> 
> The behavior was accidentally introduced in a patch described as "This is
> purely preparation for upcoming commits, there should be no code changes here.".
> As far as I can tell, that was true for the rest of that patch except for
> this one function, which has been changed to a NOP.
> 
> This patch restores the original behavior.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 8c1aeaa13954 ("drm/nouveau/pm: cosmetic changes")
Reviewed-by: Ben Skeggs <bskeggs@...hat.com>

> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c b/drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c
> index 4bef72a9d106..3fda594700e0 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/pm/nv40.c
> @@ -59,9 +59,11 @@ static void
>  nv40_perfctr_next(struct nvkm_pm *pm, struct nvkm_perfdom *dom)
>  {
>  	struct nvkm_device *device = pm->engine.subdev.device;
> -	if (pm->sequence != pm->sequence) {
> +	struct nv40_pm *nv40pm = container_of(pm, struct nv40_pm, base);
> +
> +	if (nv40pm->sequence != pm->sequence) {
>  		nvkm_wr32(device, 0x400084, 0x00000020);
> -		pm->sequence = pm->sequence;
> +		nv40pm->sequence = pm->sequence;
>  	}
>  }
>  
> 


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