linux-kernel - Re: [PATCH v2 4/4] media: tc358746: add Toshiba TC358746 Parallel to CSI-2 bridge driver

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Message-ID: <Yyl/oqZwUUb1Z0qM@paasikivi.fi.intel.com>
Date:   Tue, 20 Sep 2022 08:53:54 +0000
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Marco Felsch <m.felsch@...gutronix.de>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        mchehab@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, kishon@...com, vkoul@...nel.org,
        hverkuil@...all.nl, jacopo@...ndi.org,
        kieran.bingham+renesas@...asonboard.com,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
        kernel@...gutronix.de
Subject: Re: [PATCH v2 4/4] media: tc358746: add Toshiba TC358746 Parallel to
 CSI-2 bridge driver

Hi Marco,

On Tue, Sep 20, 2022 at 10:39:08AM +0200, Marco Felsch wrote:
> Hi Sakari,
> 
> On 22-09-19, Sakari Ailus wrote:
> > On Mon, Sep 19, 2022 at 08:37:23PM +0300, Laurent Pinchart wrote:
> > > > > > +	ctrl = v4l2_ctrl_new_int_menu(&tc358746->ctrl_hdl, NULL,
> > > > > > +				      V4L2_CID_LINK_FREQ, 0, 0,
> > > > > 
> > > > > Shouldn't the max argument be set to the number of items minus 1 ?
> > > > 
> > > > Right now I would keep it that way since the driver only supports one
> > > > link-frequencies setting. So the ctrl don't let the userspace assume
> > > > that there are more than one link-frequency.
> > > 
> > > Good point. Can you add a short comment above the call to explain this ?
> > 
> > Wouldn't it be just easier to do what Laurent suggested originally? The end
> > result is the same, isn't it, and no comment needed?
> 
> The end result depends on the device-tree given "link-frequencies"
> property. The driver currently takes only one frequency but the
> system-integrator of course can specify many more. In such case the 1st
> is used. If I go with Laurent's comment, all frequencies would be shown
> to the user-space but IMHO this shouldn't be the case since the driver
> supports only 1 frequency.

Yes, indeed. The driver can later be amended to support this.

> 
> > > 
> > > > > > +				      link_frequencies);
> > > > > > +	if (ctrl)
> > > > > > +		ctrl->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> > 
> > Now that this is a bridge, this value presumably doesn't need to change.
> 
> The value can change, e.g. if you have a few freq. to allow a wide range
> of frame sizes. This can be the case to conform the emv tests. So there
> can be a freq. for smaller frame sizes and one for larger frame sizes.

Ack.

-- 
Regards,

Sakari Ailus