linux-kernel - Re: [PATCH 09/16] media: cadence: csi2rx: Turn subdev power on before starting stream

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Date:   Tue, 6 Apr 2021 23:23:27 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Peter Ujfalusi <peter.ujfalusi@...il.com>,
        Maxime Ripard <mripard@...nel.org>,
        Benoit Parrot <bparrot@...com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Alexandre Courbot <acourbot@...omium.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Helen Koike <helen.koike@...labora.com>,
        Michael Tretter <m.tretter@...gutronix.de>,
        Peter Chen <peter.chen@....com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-phy@...ts.infradead.org>,
        <dmaengine@...r.kernel.org>, Vignesh Raghavendra <vigneshr@...com>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: Re: [PATCH 09/16] media: cadence: csi2rx: Turn subdev power on
 before starting stream

On 02/04/21 01:55PM, Laurent Pinchart wrote:
> Hi Pratyush,
> 
> Thank you for the patch.
> 
> On Tue, Mar 30, 2021 at 11:03:41PM +0530, Pratyush Yadav wrote:
> > The subdevice power needs to be turned on before the stream is started.
> > Otherwise it might not be in the proper state to stream the data. Turn
> > it off when stopping the stream.
> 
> The .s_power() operation is deprecated. Subdev drivers should control
> power internally in their .s_stream() operation, and they should use
> runtime PM to do so (this will allow usage of runtime PM autosuspend, to
> avoid expensive power off/on cycles when stopping and restarting video
> capture).

The s_power documentation in v4l2-subdev.h does not mention that it is 
depreciated. A documentation update is in order. I will send a separate 
patch to do it.

I tested this with OV5640. Not doing an s_power() operation before 
s_stream() does not work. The application freezes forever waiting for 
the first frame. So the OV5640 driver needs to be updated to use runtime 
PM to do this, right?

> 
> > Signed-off-by: Pratyush Yadav <p.yadav@...com>
> > ---
> >  drivers/media/platform/cadence/cdns-csi2rx.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/media/platform/cadence/cdns-csi2rx.c b/drivers/media/platform/cadence/cdns-csi2rx.c
> > index 7d1ac51e0698..3385e1bc213e 100644
> > --- a/drivers/media/platform/cadence/cdns-csi2rx.c
> > +++ b/drivers/media/platform/cadence/cdns-csi2rx.c
> > @@ -256,6 +256,10 @@ static int csi2rx_start(struct csi2rx_priv *csi2rx)
> >  
> >  	writel(reg, csi2rx->base + CSI2RX_STATIC_CFG_REG);
> >  
> > +	ret = v4l2_subdev_call(csi2rx->source_subdev, core, s_power, true);
> > +	if (ret && ret != -ENOIOCTLCMD)
> > +		goto err_disable_pclk;
> > +
> >  	ret = v4l2_subdev_call(csi2rx->source_subdev, video, s_stream, true);
> >  	if (ret)
> >  		goto err_disable_pclk;
> > @@ -358,6 +362,10 @@ static void csi2rx_stop(struct csi2rx_priv *csi2rx)
> >  	if (v4l2_subdev_call(csi2rx->source_subdev, video, s_stream, false))
> >  		dev_warn(csi2rx->dev, "Couldn't disable our subdev\n");
> >  
> > +	ret = v4l2_subdev_call(csi2rx->source_subdev, core, s_power, false);
> > +	if (ret && ret != -ENOIOCTLCMD)
> > +		dev_warn(csi2rx->dev, "Couldn't power off subdev\n");
> > +
> >  	if (csi2rx->dphy) {
> >  		writel(0, csi2rx->base + CSI2RX_DPHY_LANE_CTRL_REG);
> >  
> 
> -- 
> Regards,
> 
> Laurent Pinchart

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.