linux-kernel - Re: [PATCH v2 2/3] media: Add lane checks for Cadence CSI2RX

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Date:   Mon, 9 Sep 2019 12:40:49 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Jan Kotas <jank@...ence.com>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Rafal Ciepiela <rafalc@...ence.com>,
        linux-media <linux-media@...r.kernel.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] media: Add lane checks for Cadence CSI2RX

On Mon, Sep 09, 2019 at 08:12:54AM +0000, Jan Kotas wrote:
> 
> 
> > On 9 Sep 2019, at 09:51, Sakari Ailus <sakari.ailus@....fi> wrote:
> > 
> > 
> > On Mon, Sep 09, 2019 at 07:41:21AM +0000, Jan Kotas wrote:
> >> 
> >> 
> >> Hello Sakari,
> >> 
> >> Thanks for your reply.
> >>> On 6 Sep 2019, at 09:54, Sakari Ailus <sakari.ailus@....fi> wrote:
> >>> 
> >>> Hi Jan,
> >>> 
> >>> Thanks for the patchset.
> >>> 
> >>> On Thu, Sep 05, 2019 at 11:56:00AM +0100, Jan Kotas wrote:
> >>>> /*
> >>>> * Driver for Cadence MIPI-CSI2 RX Controller v1.3
> >>>> *
> >>>> - * Copyright (C) 2017 Cadence Design Systems Inc.
> >>>> + * Copyright (C) 2017-2019 Cadence Design Systems Inc.
> >>>> */
> >>>> 
> >>>> +	for (i = 0; i < csi2rx->num_lanes; i++) {
> >>>> +		if (csi2rx->lanes[i] < 1) {
> >>> 
> >>> Do you need this? v4l2_fwnode_parse_endpoint() already has a more thorough
> >>> check for the lane numbers.
> >> 
> >> I looked at the source code of v4l2_fwnode_endpoint_parse_csi2_bus
> >> and this particular case doesn’t seem to be checked.
> > 
> > Not specifically, since 0 is a valid lane number.
> > 
> > However, the driver only appears to be using the information on how many
> > lanes there are. If the hardware doesn't support lane routing, then this is
> > all you need. Otherwise additional checks should be added in case there are
> > limitations how the lanes can be routed.
> 
> The CSI2RX v1.3 does support that (CSI2RX_STATIC_CFG_REG)
> and assumes the first data lane has number 1.

Oh. I missed this. Thanks for pointing it out.

If the first data lane must be 1, then your check is still different: it
requires all the data lanes are greater than 1. Are there requireents for
the clock lane position? Looking at the driver, it seems it does not care
about the clock lane, and an educated guess gives 0 for the clock lane.

The DT binding documentation actually omits documenting the data-lanes
altogether. Please add it in a separate patch. I don't think "clock-lanes"
is needed _if_ zero is all you need, so please remove it also from the
examples.

It's actually nice to have more users for this feature. :-)

-- 
Kind regards,

Sakari Ailus