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Reply-To: kieran.bingham+renesas@ideasonboard.com
Subject: Re: [PATCH v9 2/4] media: i2c: Add MAX9286 driver
To:     Jacopo Mondi <jacopo@jmondi.org>
Cc:     Sakari Ailus <sakari.ailus@iki.fi>,
        linux-renesas-soc@vger.kernel.org, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        =?UTF-8?Q?Niklas_S=c3=b6derlund?= <niklas.soderlund@ragnatech.se>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Hyun Kwon <hyunk@xilinx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Jacopo Mondi <jacopo+renesas@jmondi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
        =?UTF-8?Q?Niklas_S=c3=b6derlund?= 
        <niklas.soderlund+renesas@ragnatech.se>
References: <20200512155105.1068064-1-kieran.bingham+renesas@ideasonboard.com>
 <20200512155105.1068064-3-kieran.bingham+renesas@ideasonboard.com>
 <20200516215103.GA857@valkosipuli.retiisi.org.uk>
 <930009cd-d887-752a-4f1f-567c795101ee@ideasonboard.com>
 <20200518123810.wsqg2a3lbbme36e7@uno.localdomain>
From:   Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Organization: Ideas on Board
Message-ID: <e898b72f-f793-6c0d-27a8-5a34c61f763e@ideasonboard.com>
Date:   Mon, 18 May 2020 14:09:45 +0100
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Hi Jacopo, Sakari,

On 18/05/2020 13:38, Jacopo Mondi wrote:
> Hi Kieran, Sakari
> 
> On Mon, May 18, 2020 at 12:45:18PM +0100, Kieran Bingham wrote:
>> Hi Sakari,
>>
>> There are only fairly minor comments here, fix ups will be included in a
>> v10.
>>
>> Is there anything major blocking integration?
>>
>> Regards
>>
>> Kieran
>>
>>
>>
>> On 16/05/2020 22:51, Sakari Ailus wrote:
>>> Hi Kieran,
>>>
>>> Thanks for the update.
>>>
>>> On Tue, May 12, 2020 at 04:51:03PM +0100, Kieran Bingham wrote:
>>>
>>> ...
>>>
>>>> +static int max9286_enum_mbus_code(struct v4l2_subdev *sd,
>>>> +				  struct v4l2_subdev_pad_config *cfg,
>>>> +				  struct v4l2_subdev_mbus_code_enum *code)
>>>> +{
>>>> +	if (code->pad || code->index > 0)
>>>> +		return -EINVAL;
>>>> +
>>>> +	code->code = MEDIA_BUS_FMT_UYVY8_2X8;
>>>
>>> Why UYVY8_2X8 and not UYVY8_1X16? In general, the single sample / pixel
>>> variant of the format is generally used on the serial busses. This choice
>>> was made when serial busses were introduced.
>>
>> Ok - I presume this doesn't really have much effect anyway, they just
>> have to match for the transmitter/receiver?
>>
>> But it makes sense to me, so I'll update to the 1x16 variant.
>>
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static struct v4l2_mbus_framefmt *
>>>> +max9286_get_pad_format(struct max9286_priv *priv,
>>>> +		       struct v4l2_subdev_pad_config *cfg,
>>>> +		       unsigned int pad, u32 which)
>>>> +{
>>>> +	switch (which) {
>>>> +	case V4L2_SUBDEV_FORMAT_TRY:
>>>> +		return v4l2_subdev_get_try_format(&priv->sd, cfg, pad);
>>>> +	case V4L2_SUBDEV_FORMAT_ACTIVE:
>>>> +		return &priv->fmt[pad];
>>>> +	default:
>>>> +		return NULL;
>>>> +	}
>>>> +}
>>>> +
>>>> +static int max9286_set_fmt(struct v4l2_subdev *sd,
>>>> +			   struct v4l2_subdev_pad_config *cfg,
>>>> +			   struct v4l2_subdev_format *format)
>>>> +{
>>>> +	struct max9286_priv *priv = sd_to_max9286(sd);
>>>> +	struct v4l2_mbus_framefmt *cfg_fmt;
>>>> +
>>>> +	if (format->pad >= MAX9286_SRC_PAD)
>>>> +		return -EINVAL;
>>>
>>> You can remove these checks; it's been already done by the caller.
>>>
>>
>> Ok.
>>
> 
> I think this shold be kept. The core validates that the pad number is
> valid, but we're here checking that set_fmt has been called on a sink
> pad [0-3], returning -EINVAL if set_fmt (and get_ftm as well) are
> called on the source one.
> 

Indeed, this is actually preventing get/set format on the intermediate
(multiplexed) stream. But it is "breaking" link validation (or
preventing it from happening maybe?), which is defaulting 'open' ...
that might be a problem we need to look at, but as we don't have a real
multiplexed stream support implementation then that's perhaps more
difficult to give a 'correct' answer.


> My question now is how does link validation work, if get_fmt() is not
> allowed on the source pad :/ ? Anyway, I would keep this check for
> set_fmt (maybe make it an == to address Sakari's comment).


Ok - so as long as we return -EINVAL for the MAX9286_SRC_PAD, then
v4l2_subdev_link_validate() will fail on
v4l2_subdev_link_validate_get_format() for that pad, which causes a return 0

(v4l2_subdev_link_validate defaulting to success if it can't get both pads)

We could convert this to:

/*
 * \todo: Prevent validation of the source pad, as it represents a
 * multiplexed stream, and we do not have multiplexed stream support in
 * V4L2 yet.
 */
if (format->pad == MAX9286_SRC_PAD)


Or we could call this a blocker. Which will make me sad, as I really
want to be able to have a baseline for development for this driver, but
I've been calling out for "What blockers prevent this driver from being
merged" since February so if this is it - so be it...


Sakari - is this a blocking issue for you? Or can we consider this a
topic that we (already know) needs visiting as part of V4L2 Multiplexed
stream support.

We already know of course that this driver is taking liberties due to
the lack of multiplexed stream support, and requires the receiver to
assume that each camera is on a different (consecutive?) VC.


Or perhaps - to enforce validation, we could have the get_fmt call pass
on the bus format of the first camera link ?

Thoughts anyone?


> 
> Thanks
>   j
> 
>>
>>> ...
>>>
>>>> +static int max9286_parse_dt(struct max9286_priv *priv)
>>>> +{
>>>> +	struct device *dev = &priv->client->dev;
>>>> +	struct device_node *i2c_mux;
>>>> +	struct device_node *node = NULL;
>>>> +	unsigned int i2c_mux_mask = 0;
>>>> +
>>>> +	of_node_get(dev->of_node);
>>>> +	i2c_mux = of_find_node_by_name(dev->of_node, "i2c-mux");
>>>> +	if (!i2c_mux) {
>>>> +		dev_err(dev, "Failed to find i2c-mux node\n");
>>>> +		of_node_put(dev->of_node);
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>> +	/* Identify which i2c-mux channels are enabled */
>>>> +	for_each_child_of_node(i2c_mux, node) {
>>>> +		u32 id = 0;
>>>> +
>>>> +		of_property_read_u32(node, "reg", &id);
>>>> +		if (id >= MAX9286_NUM_GMSL)
>>>> +			continue;
>>>> +
>>>> +		if (!of_device_is_available(node)) {
>>>> +			dev_dbg(dev, "Skipping disabled I2C bus port %u\n", id);
>>>> +			continue;
>>>> +		}
>>>> +
>>>> +		i2c_mux_mask |= BIT(id);
>>>> +	}
>>>> +	of_node_put(node);
>>>> +	of_node_put(i2c_mux);
>>>> +
>>>> +	/* Parse the endpoints */
>>>> +	for_each_endpoint_of_node(dev->of_node, node) {
>>>> +		struct max9286_source *source;
>>>> +		struct of_endpoint ep;
>>>> +
>>>> +		of_graph_parse_endpoint(node, &ep);
>>>> +		dev_dbg(dev, "Endpoint %pOF on port %d",
>>>> +			ep.local_node, ep.port);
>>>> +
>>>> +		if (ep.port > MAX9286_NUM_GMSL) {
>>>> +			dev_err(dev, "Invalid endpoint %s on port %d",
>>>> +				of_node_full_name(ep.local_node), ep.port);
>>>> +			continue;
>>>> +		}
>>>> +
>>>> +		/* For the source endpoint just parse the bus configuration. */
>>>> +		if (ep.port == MAX9286_SRC_PAD) {
>>>> +			struct v4l2_fwnode_endpoint vep = {
>>>> +				.bus_type = V4L2_MBUS_CSI2_DPHY
>>>> +			};
>>>> +			int ret;
>>>> +
>>>> +			ret = v4l2_fwnode_endpoint_parse(
>>>> +					of_fwnode_handle(node), &vep);
>>>> +			if (ret) {
>>>> +				of_node_put(node);
>>>> +				of_node_put(dev->of_node);
>>>> +				return ret;
>>>> +			}
>>>> +
>>>> +			if (vep.bus_type != V4L2_MBUS_CSI2_DPHY) {
>>>
>>> This won't happen, the bus type will stay if you set it to a non-zero
>>> value.
>>
>>
>> Ok - I'll remove this check.
>>
>>
>>>
>>>> +				dev_err(dev,
>>>> +					"Media bus %u type not supported\n",
>>>> +					vep.bus_type);
>>>> +				v4l2_fwnode_endpoint_free(&vep);
>>>> +				of_node_put(node);
>>>> +				of_node_put(dev->of_node);
>>>> +				return -EINVAL;
>>>> +			}
>>>> +
>>>> +			priv->csi2_data_lanes =
>>>> +				vep.bus.mipi_csi2.num_data_lanes;
>>>> +			v4l2_fwnode_endpoint_free(&vep);
>>>
>>> No need to call this unless you use v4l2_fwnode_endpoint_alloc_parse().
>>>
>>> And as you don't, you also won't know which frequencies are known to be
>>> safe to use. That said, perhaps where this device is used having a random
>>> frequency on that bus could not be an issue. Perhaps.
>>
>> Does this generate a range? or a list of static supported frequencies?
>>
>> We configure the pixel clock based upon the number of cameras connected,
>> and their pixel rates etc ...
>>
>> Are you saying that the frequency of this clock should be validated to
>> be a specific range? or are you talking about a different frequency?
>>
>>
>> For now I'll remove the v4l2_fwnode_endpoint_alloc_parse().
>>
>>
>>
>>>> +
>>>> +			continue;
>>>> +		}
>>>> +
>>>> +		/* Skip if the corresponding GMSL link is unavailable. */
>>>> +		if (!(i2c_mux_mask & BIT(ep.port)))
>>>> +			continue;
>>>> +
>>>> +		if (priv->sources[ep.port].fwnode) {
>>>> +			dev_err(dev,
>>>> +				"Multiple port endpoints are not supported: %d",
>>>> +				ep.port);
>>>> +
>>>> +			continue;
>>>> +		}
>>>> +
>>>> +		source = &priv->sources[ep.port];
>>>> +		source->fwnode = fwnode_graph_get_remote_endpoint(
>>>> +						of_fwnode_handle(node));
>>>> +		if (!source->fwnode) {
>>>> +			dev_err(dev,
>>>> +				"Endpoint %pOF has no remote endpoint connection\n",
>>>> +				ep.local_node);
>>>> +
>>>> +			continue;
>>>> +		}
>>>> +
>>>> +		priv->source_mask |= BIT(ep.port);
>>>> +		priv->nsources++;
>>>> +	}
>>>> +	of_node_put(node);
>>>> +	of_node_put(dev->of_node);
>>>> +
>>>> +	priv->route_mask = priv->source_mask;
>>>> +
>>>> +	return 0;
>>>> +}
>>>
>>