Re: [PATCH v2 10/18] media: cadence: csi2rx: Populate subdev devnode

From: Pratyush Yadav <p.yadav@ti.com>
To: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Cc: Maxime Ripard <mripard@kernel.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	Vinod Koul <vkoul@kernel.org>,
	Peter Ujfalusi <peter.ujfalusi@gmail.com>,
	Steve Longerbeam <slongerbeam@gmail.com>,
	Benoit Parrot <bparrot@ti.com>, <linux-media@vger.kernel.org>,
	<devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-phy@lists.infradead.org>, <dmaengine@vger.kernel.org>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Chunfeng Yun <chunfeng.yun@mediatek.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Subject: Re: [PATCH v2 10/18] media: cadence: csi2rx: Populate subdev devnode
Date: Fri, 28 May 2021 12:54:03 +0530	[thread overview]
Message-ID: <20210528072401.2vdrtjdiepnr72vv@ti.com> (raw)
In-Reply-To: <9c38a72c-18e8-1e54-b3b4-85ff5d47857a@ideasonboard.com>

On 28/05/21 10:16AM, Tomi Valkeinen wrote:
> On 26/05/2021 18:23, Pratyush Yadav wrote:
> > The devnode can be used by media-ctl and other userspace tools to
> > perform configurations on the subdev. Without it, media-ctl returns
> > ENOENT when setting format on the sensor subdev.
> > 
> > Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
> > ---
> > 
> > (no changes since v1)
> > 
> >   drivers/media/platform/cadence/cdns-csi2rx.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/media/platform/cadence/cdns-csi2rx.c b/drivers/media/platform/cadence/cdns-csi2rx.c
> > index 1df21f462f3c..49bed63d5faa 100644
> > --- a/drivers/media/platform/cadence/cdns-csi2rx.c
> > +++ b/drivers/media/platform/cadence/cdns-csi2rx.c
> > @@ -613,6 +613,7 @@ static int csi2rx_probe(struct platform_device *pdev)
> >   	csi2rx->pads[CSI2RX_PAD_SINK].flags = MEDIA_PAD_FL_SINK;
> >   	for (i = CSI2RX_PAD_SOURCE_STREAM0; i < CSI2RX_PAD_MAX; i++)
> >   		csi2rx->pads[i].flags = MEDIA_PAD_FL_SOURCE;
> > +	csi2rx->subdev.flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> >   	ret = media_entity_pads_init(&csi2rx->subdev.entity, CSI2RX_PAD_MAX,
> >   				     csi2rx->pads);
> > 
> 
> I don't understand this one. There's nothing to configure in cdns-csi2rx
> from userspace, as far as I can see, so why is the dev node needed? And why
> would the lack of csi2rx dev node cause sensor subdev config to fail?

Sensor config does not fail. But when I run media-ctl to set the format 
on /dev/media0, I get an error message that comes because the devnode 
for the bridge does not exist. I was not 100% sure about this patch but 
I figured if media-ctl expects it then it should be exposed.

I don't mind dropping this patch. Just want to make sure what the right 
thing to do here is. Should every element of the pipeline have a devnode 
or not?

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.