linux-kernel - Re: [PATCH v5 4/4] media: imx-mipi-csis: Support active data lanes differing from maximum

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Message-ID: <20251026211107.GF1025@pendragon.ideasonboard.com>
Date: Sun, 26 Oct 2025 23:11:07 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Isaac Scott <isaac.scott@...asonboard.com>, mchehab@...nel.org,
	rmfrfs@...il.com, martink@...teo.de, kernel@...i.sm,
	shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
	festevam@...il.com, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, Frank.Li@....com
Subject: Re: [PATCH v5 4/4] media: imx-mipi-csis: Support active data lanes
 differing from maximum

On Wed, Oct 22, 2025 at 02:13:09PM +0300, Sakari Ailus wrote:
> On Wed, Oct 22, 2025 at 11:22:28AM +0100, Isaac Scott wrote:
> > Call on v4l2_get_active_data_lanes() to check if the driver reports that
> > the number of lanes actively used by the MIPI CSI transmitter differs to
> > the maximum defined in device tree.
> > 
> > If the number of active data lanes reported by the driver is invalid, or
> > the operation is not supported, fall back to the number of allowed data
> > lanes.
> > 
> > Signed-off-by: Isaac Scott <isaac.scott@...asonboard.com>
> > ---
> >  drivers/media/platform/nxp/imx-mipi-csis.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/media/platform/nxp/imx-mipi-csis.c b/drivers/media/platform/nxp/imx-mipi-csis.c
> > index 838a1ad123b5..637ef6e614fa 100644
> > --- a/drivers/media/platform/nxp/imx-mipi-csis.c
> > +++ b/drivers/media/platform/nxp/imx-mipi-csis.c
> > @@ -1034,6 +1034,10 @@ static int mipi_csis_s_stream(struct v4l2_subdev *sd, int enable)
> >  	format = v4l2_subdev_state_get_format(state, CSIS_PAD_SINK);
> >  	csis_fmt = find_csis_format(format->code);
> >  
> > +	ret = v4l2_get_active_data_lanes(csis->source.pad,
> > +					 csis->bus.num_data_lanes);
> > +	csis->num_data_lanes = ret < 0 ? csis->bus.num_data_lanes : ret;
> 
> I guess this works but should we return an error here instead?
> 
> Alternatively, the function could always return some number of lanes as
> well (with a printed warning on error). I think I'd do the former though.

Agreed, I would return an error.

> > +
> >  	ret = mipi_csis_calculate_params(csis, csis_fmt);
> >  	if (ret < 0)
> >  		goto err_unlock;

-- 
Regards,

Laurent Pinchart