linux-kernel - Re: [PATCH v4 14/23] drm/tilcdc: Provide ddc symlink in connector sysfs directory

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Message-ID: <20190723151939.GA13718@ravnborg.org>
Date:   Tue, 23 Jul 2019 17:19:39 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Andrzej Pietrasiewicz <andrzej.p@...labora.com>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Shawn Guo <shawnguo@...nel.org>, kernel@...labora.com,
        linux-samsung-soc@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, Sean Paul <sean@...rly.run>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        Kukjin Kim <kgene@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Dave Airlie <airlied@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jonas Karlman <jonas@...boo.se>, linux-arm-msm@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, Jyri Sarha <jsarha@...com>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Mamta Shukla <mamtashukla555@...il.com>,
        linux-mediatek@...ts.infradead.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        linux-tegra@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Vincent Abriou <vincent.abriou@...com>,
        linux-arm-kernel@...ts.infradead.org,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        amd-gfx@...ts.freedesktop.org,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Douglas Anderson <dianders@...omium.org>,
        Todor Tomov <todor.tomov@...aro.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Huang Rui <ray.huang@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Alex Deucher <alexander.deucher@....com>,
        freedreno@...ts.freedesktop.org,
        Christian König <christian.koenig@....com>,
        Gerd Hoffmann <kraxel@...hat.com>
Subject: Re: [PATCH v4 14/23] drm/tilcdc: Provide ddc symlink in connector
 sysfs directory

Hi Andrej.

On Tue, Jul 23, 2019 at 02:44:50PM +0200, Andrzej Pietrasiewicz wrote:
> Hi Sam,
> 
> W dniu 23.07.2019 o 11:05, Sam Ravnborg pisze:
> > Hi Andrzej
> > 
> > On Thu, Jul 11, 2019 at 01:26:41PM +0200, Andrzej Pietrasiewicz wrote:
> > > Use the ddc pointer provided by the generic connector.
> > > 
> > > Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
> > > ---
> > >   drivers/gpu/drm/tilcdc/tilcdc_tfp410.c | 1 +
> > >   1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/gpu/drm/tilcdc/tilcdc_tfp410.c b/drivers/gpu/drm/tilcdc/tilcdc_tfp410.c
> > > index 62d014c20988..c373edb95666 100644
> > > --- a/drivers/gpu/drm/tilcdc/tilcdc_tfp410.c
> > > +++ b/drivers/gpu/drm/tilcdc/tilcdc_tfp410.c
> > > @@ -219,6 +219,7 @@ static struct drm_connector *tfp410_connector_create(struct drm_device *dev,
> > >   	tfp410_connector->mod = mod;
> > >   	connector = &tfp410_connector->base;
> > > +	connector->ddc = mod->i2c;
> > >   	drm_connector_init(dev, connector, &tfp410_connector_funcs,
> > >   			DRM_MODE_CONNECTOR_DVID);
> > 
> > When reading this code, it looks strange that we set connector->ddc
> > *before* the call to init the connector.
> > One could risk that drm_connector_init() used memset(..) to clear all
> > fields or so, and it would break this order.
> 
> I verified the code of drm_connector_init() and cannot find any memset()
> invocations there. What is your actual concern?
My concern is that drm_connector_init() maybe sometime in the future
will init all fileds in drm_connector, so we loose any assingments
done to drm_connector from *before* we called the init function.

Moving the assignment to after drm_connector_init() would not
let us depend on the actual implmentation of drm_connector_init().

	Sam