linux-kernel - RE: [PATCH v8 1/2] media: dt-bindings: media: xilinx: Add Xilinx MIPI CSI-2 Rx Subsystem

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Date:   Thu, 6 Jun 2019 12:23:08 +0000
From:   Vishal Sagar <vsagar@...inx.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
CC:     Vishal Sagar <vishal.sagar@...inx.com>,
        Hyun Kwon <hyunk@...inx.com>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Michal Simek <michals@...inx.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "hans.verkuil@...co.com" <hans.verkuil@...co.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dinesh Kumar <dineshk@...inx.com>,
        Sandip Kothari <sandipk@...inx.com>,
        Luca Ceresoli <luca@...aceresoli.net>,
        Jacopo Mondi <jacopo@...ndi.org>
Subject: RE: [PATCH v8 1/2] media: dt-bindings: media: xilinx: Add Xilinx MIPI
 CSI-2 Rx Subsystem

Hi Sakari,

> -----Original Message-----
> From: Sakari Ailus [mailto:sakari.ailus@...ux.intel.com]
> Sent: Thursday, June 06, 2019 5:43 PM
> To: Vishal Sagar <vsagar@...inx.com>
> Cc: Vishal Sagar <vishal.sagar@...inx.com>; Hyun Kwon <hyunk@...inx.com>;
> laurent.pinchart@...asonboard.com; mchehab@...nel.org;
> robh+dt@...nel.org; mark.rutland@....com; Michal Simek
> <michals@...inx.com>; linux-media@...r.kernel.org;
> devicetree@...r.kernel.org; hans.verkuil@...co.com; linux-arm-
> kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; Dinesh Kumar
> <dineshk@...inx.com>; Sandip Kothari <sandipk@...inx.com>; Luca Ceresoli
> <luca@...aceresoli.net>; Jacopo Mondi <jacopo@...ndi.org>
> Subject: Re: [PATCH v8 1/2] media: dt-bindings: media: xilinx: Add Xilinx MIPI
> CSI-2 Rx Subsystem
> 
> Hi Vishal,
> 
> On Thu, Jun 06, 2019 at 11:54:19AM +0000, Vishal Sagar wrote:
> > Hi Sakari,
> >
> > > -----Original Message-----
> > > From: Sakari Ailus [mailto:sakari.ailus@...ux.intel.com]
> > > Sent: Wednesday, June 05, 2019 12:54 AM
> > > To: Vishal Sagar <vishal.sagar@...inx.com>
> > > Cc: Hyun Kwon <hyunk@...inx.com>; laurent.pinchart@...asonboard.com;
> > > mchehab@...nel.org; robh+dt@...nel.org; mark.rutland@....com;
> Michal
> > > Simek <michals@...inx.com>; linux-media@...r.kernel.org;
> > > devicetree@...r.kernel.org; hans.verkuil@...co.com; linux-arm-
> > > kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; Dinesh Kumar
> > > <dineshk@...inx.com>; Sandip Kothari <sandipk@...inx.com>; Luca Ceresoli
> > > <luca@...aceresoli.net>; Jacopo Mondi <jacopo@...ndi.org>
> > > Subject: Re: [PATCH v8 1/2] media: dt-bindings: media: xilinx: Add Xilinx
> MIPI
> > > CSI-2 Rx Subsystem
> > >
> > > EXTERNAL EMAIL
> > >
> > > Hi Vishal,
> > >
> > > On Mon, Jun 03, 2019 at 03:29:30PM +0530, Vishal Sagar wrote:
> > >
> > > > +Optional properties:
> > > > +--------------------
> > > > +- .
> > > > +  Without this property the driver won't be loaded as IP won't be able to
> > > generate
> > > > +  media bus format compliant stream output.
> > >
> > > I think we previously concluded that the format will be just different in
> > > this case. So the description appears incorrect.
> > >
> >
> > Referring to your email https://lkml.org/lkml/2019/3/22/1823 in response to
> v6 patches,
> > if the video format bridge is not enabled, then the way in which pixels are
> transported on
> > the bus don't correspond to the existing media bus formats in Linux.
> >
> > If not loading the driver is incorrect way, is it ok for the driver to allow same
> media bus format
> > for packed and unpacked data type on the sink pad?
> >
> > Or is it ok for the driver to not validate the media bus format set on the sink
> pad?
> 
> Taking a fresh look at the issue --- usually such unpacking is done by the
> DMA engine, or the same device contains both the CSI-2 RX and DMA. But here
> it actually affects the input of that DMA engine. You're right in saying we
> don't have format definitions from which you could tell which case it is,
> and we also don't have other pre-existing means to tell them apart.
> 
> Feel free to keep the check in the driver, but we can't refer to the driver
> loading in DT binding documentation: this is really not supposed to be
> related to that driver, or even Linux at all.
> 

Ok got it. The description here shouldn't be specific to driver.
I will keep the check in driver.

> How about changing this to:
> 
> xlnx,vfb: Present when Video Format Bridge is enabled in IP configuration.
> 
> That'd be aligned with the other properties and would more accurately
> convey what this means.

Agree this is a good way to define the property. I will update it the description as mentioned here.

> 
> --
> Kind regards,
> 
> Sakari Ailus
> sakari.ailus@...ux.intel.com

Regards
Vishal Sagar