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SubjectRe: [PATCH v4 3/4] media: i2c: Add MAX9286 driver
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Hi Kieran,

On 14/11/18 01:46, Kieran Bingham wrote:
> Hi Luca,
>
> Thank you for your review,
>
> On 13/11/2018 14:49, Luca Ceresoli wrote:
>> Hi Kieran, All,
>>
>> below a few minor questions, and a big one at the bottom.
>>
>> On 02/11/18 16:47, Kieran Bingham wrote:
>>> From: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>>>
>>> The MAX9286 is a 4-channel GMSL deserializer with coax or STP input and
>>> CSI-2 output. The device supports multicamera streaming applications,
>>> and features the ability to synchronise the attached cameras.
>>>
>>> CSI-2 output can be configured with 1 to 4 lanes, and a control channel
>>> is supported over I2C, which implements an I2C mux to facilitate
>>> communications with connected cameras across the reverse control
>>> channel.
>>>
>>> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
>>> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
>>> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
>>> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
>>
>> [...]
>>
>>> +struct max9286_device {
>>> + struct i2c_client *client;
>>> + struct v4l2_subdev sd;
>>> + struct media_pad pads[MAX9286_N_PADS];
>>> + struct regulator *regulator;
>>> + bool poc_enabled;
>>> + int streaming;
>>> +
>>> + struct i2c_mux_core *mux;
>>> + unsigned int mux_channel;
>>> +
>>> + struct v4l2_ctrl_handler ctrls;
>>> +
>>> + struct v4l2_mbus_framefmt fmt[MAX9286_N_SINKS];
>>
>> 5 pads, 4 formats. Why does the source node have no fmt?
>
> The source pad is a CSI2 link - so a 'frame format' would be inappropriate.

Ok, thanks for the clarification.

>>> +static int max9286_probe(struct i2c_client *client,
>>> + const struct i2c_device_id *did)
>>> +{
>>> + struct max9286_device *dev;
>>> + unsigned int i;
>>> + int ret;
>>> +
>>> + dev = kzalloc(sizeof(*dev), GFP_KERNEL);
>>> + if (!dev)
>>> + return -ENOMEM;
>>> +
>>> + dev->client = client;
>>> + i2c_set_clientdata(client, dev);
>>> +
>>> + for (i = 0; i < MAX9286_N_SINKS; i++)
>>> + max9286_init_format(&dev->fmt[i]);
>>> +
>>> + ret = max9286_parse_dt(dev);
>>> + if (ret)
>>> + return ret;
>>> +
>>> + dev->regulator = regulator_get(&client->dev, "poc");
>>> + if (IS_ERR(dev->regulator)) {
>>> + if (PTR_ERR(dev->regulator) != -EPROBE_DEFER)
>>> + dev_err(&client->dev,
>>> + "Unable to get PoC regulator (%ld)\n",
>>> + PTR_ERR(dev->regulator));
>>> + ret = PTR_ERR(dev->regulator);
>>> + goto err_free;
>>> + }
>>> +
>>> + /*
>>> + * We can have multiple MAX9286 instances on the same physical I2C
>>> + * bus, and I2C children behind ports of separate MAX9286 instances
>>> + * having the same I2C address. As the MAX9286 starts by default with
>>> + * all ports enabled, we need to disable all ports on all MAX9286
>>> + * instances before proceeding to further initialize the devices and
>>> + * instantiate children.
>>> + *
>>> + * Start by just disabling all channels on the current device. Then,
>>> + * if all other MAX9286 on the parent bus have been probed, proceed
>>> + * to initialize them all, including the current one.
>>> + */
>>> + max9286_i2c_mux_close(dev);
>>> +
>>> + /*
>>> + * The MAX9286 initialises with auto-acknowledge enabled by default.
>>> + * This means that if multiple MAX9286 devices are connected to an I2C
>>> + * bus, another MAX9286 could ack I2C transfers meant for a device on
>>> + * the other side of the GMSL links for this MAX9286 (such as a
>>> + * MAX9271). To prevent that disable auto-acknowledge early on; it
>>> + * will be enabled later as needed.
>>> + */
>>> + max9286_configure_i2c(dev, false);
>>> +
>>> + ret = device_for_each_child(client->dev.parent, &client->dev,
>>> + max9286_is_bound);
>>> + if (ret)
>>> + return 0;
>>> +
>>> + dev_dbg(&client->dev,
>>> + "All max9286 probed: start initialization sequence\n");
>>> + ret = device_for_each_child(client->dev.parent, NULL,
>>> + max9286_init);
>>
>> I can't manage to like this initialization sequence, sorry. If at all
>> possible, each max9286 should initialize itself independently from each
>> other, like any normal driver.
>
> Yes, I think we're in agreement here, but unfortunately this section is
> a workaround for the fact that our devices share a common address space.
>
> We (currently) *must* disable both devices before we start the
> initialisation process for either on our platform currently...

The model I proposed in my review to patch 1/4 (split remote physical
address from local address pool) allows to avoid this workaround.

> That said - I think this section needs to be removed from the upstream
> part at least for now. I think we should probably carry this
> 'workaround' separately.
>
> This part is the core issue that I talked about in my presentation at
> ALS-Japan [0]
>
> [0] https://sched.co/EaXa

Oh, interesting, I hadn't noticed that you gave this talk -- at the same
conference as Vladimir's talk! No video recording apparently, but are
slides available at least?

>> First, it requires that each chip on the remote side can configure its
>> own slave address. Not all chips do.
>>
>> Second, using a static i2c address map does not scale well and limits
>> hotplugging, as I discussed in my reply to patch 1/4. The problem should
>> be solvable cleanly if the MAX9286 supports address translation like the
>> TI chips.
>
> I don't think we can treat GMSL as hot-pluggable currently ... But as we
> discussed - I see that we should think about this for FPD-Link

I've been mixing hotplug and DT overlays and that generated confusion,
sorry. My point exists even with no hotplug, see the reply to patch 1/4.

--
Luca

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