Re: [PATCH v2 5/9] drm/nouveau: Use drm_connector_for_each_possible_encoder()

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	kbuild@01.org, kbuild-all@01.org, nouveau@lists.freedesktop.org,
	Ben Skeggs <bskeggs@redhat.com>
Subject: Re: [PATCH v2 5/9] drm/nouveau: Use drm_connector_for_each_possible_encoder()
Date: Mon, 2 Jul 2018 16:04:45 +0300	[thread overview]
Message-ID: <20180702130445.GI5565@intel.com> (raw)
In-Reply-To: <20180630191221.a6o6gr7wdbjckkwm@mwanda>

On Sat, Jun 30, 2018 at 10:12:21PM +0300, Dan Carpenter wrote:
> Hi Ville,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> url:    https://github.com/0day-ci/linux/commits/Ville-Syrjala/drm-Third-attempt-at-fixing-the-fb-helper-best_encoder-mess/20180629-014202
> base:   git://people.freedesktop.org/~airlied/linux.git drm-next
> 
> smatch warnings:
> drivers/gpu/drm/nouveau/nouveau_connector.c:461 nouveau_connector_ddc_detect() error: uninitialized symbol 'nv_encoder'.
> 
> # https://github.com/0day-ci/linux/commit/7ec8bb65386edfb0b2bdc8e8391eb5e6eac44c06
> git remote add linux-review https://github.com/0day-ci/linux
> git remote update linux-review
> git checkout 7ec8bb65386edfb0b2bdc8e8391eb5e6eac44c06
> vim +/nv_encoder +461 drivers/gpu/drm/nouveau/nouveau_connector.c
> 
> 6ee738610 Ben Skeggs      2009-12-11  407  
> 8777c5c11 Ben Skeggs      2014-06-06  408  static struct nouveau_encoder *
> 8777c5c11 Ben Skeggs      2014-06-06  409  nouveau_connector_ddc_detect(struct drm_connector *connector)
> 6ee738610 Ben Skeggs      2009-12-11  410  {
> 6ee738610 Ben Skeggs      2009-12-11  411  	struct drm_device *dev = connector->dev;
> 1a1841d30 Ben Skeggs      2012-12-10  412  	struct nouveau_connector *nv_connector = nouveau_connector(connector);
> 77145f1cb Ben Skeggs      2012-07-31  413  	struct nouveau_drm *drm = nouveau_drm(dev);
> 1167c6bc5 Ben Skeggs      2016-05-18  414  	struct nvkm_gpio *gpio = nvxx_gpio(&drm->client.device);
> 8777c5c11 Ben Skeggs      2014-06-06  415  	struct nouveau_encoder *nv_encoder;
> 6d385c0aa Rob Clark       2014-07-17  416  	struct drm_encoder *encoder;
> 1a1841d30 Ben Skeggs      2012-12-10  417  	int i, panel = -ENODEV;
> 1a1841d30 Ben Skeggs      2012-12-10  418  
> 1a1841d30 Ben Skeggs      2012-12-10  419  	/* eDP panels need powering on by us (if the VBIOS doesn't default it
> 1a1841d30 Ben Skeggs      2012-12-10  420  	 * to on) before doing any AUX channel transactions.  LVDS panel power
> 1a1841d30 Ben Skeggs      2012-12-10  421  	 * is handled by the SOR itself, and not required for LVDS DDC.
> 1a1841d30 Ben Skeggs      2012-12-10  422  	 */
> 1a1841d30 Ben Skeggs      2012-12-10  423  	if (nv_connector->type == DCB_CONNECTOR_eDP) {
> 2ea7249fe Ben Skeggs      2015-08-20  424  		panel = nvkm_gpio_get(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff);
> 1a1841d30 Ben Skeggs      2012-12-10  425  		if (panel == 0) {
> 2ea7249fe Ben Skeggs      2015-08-20  426  			nvkm_gpio_set(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff, 1);
> 1a1841d30 Ben Skeggs      2012-12-10  427  			msleep(300);
> 1a1841d30 Ben Skeggs      2012-12-10  428  		}
> 1a1841d30 Ben Skeggs      2012-12-10  429  	}
> 6ee738610 Ben Skeggs      2009-12-11  430  
> 7ec8bb653 Ville Syrjälä   2018-06-28  431  	drm_connector_for_each_possible_encoder(connector, encoder, i) {
> 6d385c0aa Rob Clark       2014-07-17  432  		nv_encoder = nouveau_encoder(encoder);
>                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> If we enter the loop that means nv_encoder is non-NULL.  Smatch can't
> prove that we always enter the loop in this case for whatever reason but
> my guess is that we always do.
> 
> 4ca2b7120 Francisco Jerez 2010-08-08  433  
> 8777c5c11 Ben Skeggs      2014-06-06  434  		if (nv_encoder->dcb->type == DCB_OUTPUT_DP) {
> 8777c5c11 Ben Skeggs      2014-06-06  435  			int ret = nouveau_dp_detect(nv_encoder);
> 52aa30f25 Ben Skeggs      2016-11-04  436  			if (ret == NOUVEAU_DP_MST)
> 52aa30f25 Ben Skeggs      2016-11-04  437  				return NULL;
> 52aa30f25 Ben Skeggs      2016-11-04  438  			if (ret == NOUVEAU_DP_SST)
> 8777c5c11 Ben Skeggs      2014-06-06  439  				break;
> 8777c5c11 Ben Skeggs      2014-06-06  440  		} else
> 39c1c9011 Lukas Wunner    2016-01-11  441  		if ((vga_switcheroo_handler_flags() &
> 39c1c9011 Lukas Wunner    2016-01-11  442  		     VGA_SWITCHEROO_CAN_SWITCH_DDC) &&
> 39c1c9011 Lukas Wunner    2016-01-11  443  		    nv_encoder->dcb->type == DCB_OUTPUT_LVDS &&
> 39c1c9011 Lukas Wunner    2016-01-11  444  		    nv_encoder->i2c) {
> 39c1c9011 Lukas Wunner    2016-01-11  445  			int ret;
> 39c1c9011 Lukas Wunner    2016-01-11  446  			vga_switcheroo_lock_ddc(dev->pdev);
> 39c1c9011 Lukas Wunner    2016-01-11  447  			ret = nvkm_probe_i2c(nv_encoder->i2c, 0x50);
> 39c1c9011 Lukas Wunner    2016-01-11  448  			vga_switcheroo_unlock_ddc(dev->pdev);
> 39c1c9011 Lukas Wunner    2016-01-11  449  			if (ret)
> 39c1c9011 Lukas Wunner    2016-01-11  450  				break;
> 39c1c9011 Lukas Wunner    2016-01-11  451  		} else
> 8777c5c11 Ben Skeggs      2014-06-06  452  		if (nv_encoder->i2c) {
> 2aa5eac51 Ben Skeggs      2015-08-20  453  			if (nvkm_probe_i2c(nv_encoder->i2c, 0x50))
> 1a1841d30 Ben Skeggs      2012-12-10  454  				break;
> 6ee738610 Ben Skeggs      2009-12-11  455  		}
> 6ee738610 Ben Skeggs      2009-12-11  456  	}
> 6ee738610 Ben Skeggs      2009-12-11  457  
> 1a1841d30 Ben Skeggs      2012-12-10  458  	/* eDP panel not detected, restore panel power GPIO to previous
> 1a1841d30 Ben Skeggs      2012-12-10  459  	 * state to avoid confusing the SOR for other output types.
> 1a1841d30 Ben Skeggs      2012-12-10  460  	 */
> 8777c5c11 Ben Skeggs      2014-06-06 @461  	if (!nv_encoder && panel == 0)
>                                                     ^^^^^^^^^^^
> So testing for NULL doesn't make sense.  It's either non-NULL if we
> entered the loop at least once or it's uninitialized if we didn't enter
> the loop.

Yeah, seems like a bogus check. I suppose in theory you could have a
connector with no encoders, although I can't think of any good reason
why anyone would do that.

> 
> 2ea7249fe Ben Skeggs      2015-08-20  462  		nvkm_gpio_set(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff, panel);
> 1a1841d30 Ben Skeggs      2012-12-10  463  
> 8777c5c11 Ben Skeggs      2014-06-06  464  	return nv_encoder;
> 6ee738610 Ben Skeggs      2009-12-11  465  }
> 6ee738610 Ben Skeggs      2009-12-11  466  
> 
> 
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

-- 
Ville Syrjälä
Intel
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