Date:   Mon, 25 Mar 2019 12:14:05 +0000
From:   Mickael GUENE <mickael.guene@...com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
CC:     Sakari Ailus <sakari.ailus@....fi>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matt Ranostay <matt.ranostay@...sulko.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ben Kao <ben.kao@...el.com>,
        Todor Tomov <todor.tomov@...aro.org>,
        Rui Miguel Silva <rui.silva@...aro.org>,
        "Akinobu Mita" <akinobu.mita@...il.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        "Jason Chen" <jasonx.z.chen@...el.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Tianshu Qiu <tian.shu.qiu@...el.com>,
        Bingbu Cao <bingbu.cao@...el.com>
Subject: Re: [PATCH v1 2/3] media:st-mipid02: MIPID02 CSI-2 to PARALLEL bridge
 driver

Hi Sakari,

On 3/25/19 12:17, Sakari Ailus wrote:
> Hi Mickael,
> 
> On Mon, Mar 18, 2019 at 09:57:44AM +0000, Mickael GUENE wrote:
>> Hi Sakari,
>>
>> Thanks for your review. Find my comments below.
>>
>> On 3/16/19 23:14, Sakari Ailus wrote:
> ...
>>>> +static struct v4l2_subdev *mipid02_find_sensor(struct mipid02_dev *bridge)
>>>> +{
>>>> +	struct media_device *mdev = bridge->sd.v4l2_dev->mdev;
>>>> +	struct media_entity *entity;
>>>> +
>>>> +	if (!mdev)
>>>> +		return NULL;
>>>> +
>>>> +	media_device_for_each_entity(entity, mdev)
>>>> +		if (entity->function == MEDIA_ENT_F_CAM_SENSOR)
>>>> +			return media_entity_to_v4l2_subdev(entity);
>>>
>>> Hmm. Could you instead use the link state to determine which of the
>>> receivers is active? You'll need one more pad, and then you'd had 1:1
>>> mapping between ports and pads.
>>>
>>  Goal here is not to detect which of the receivers is active but to find
>> sensor in case there are others sub-dev in chain (for example a 
>> serializer/deserializer as found in cars).
> 
> You shouldn't make assumptions on the rest of the pipeline beyond the
> device that's directly connected. You might not even have a camera there.
> 
 I have also seen your answer to '[PATCH v2 2/2] media:st-mipid02: MIPID02 CSI-2 to PARALLEL bridge driver'
concerning support of set_fmt, get_fmt and link_validate.
 My initial idea was to avoid to avoid to implement them and to avoid media ctrl configuration. According
to your remark is seems a bad idea. Right ?
 In that case I have to also implement enum_mbus_code ?
 I will drop this code and use connected device only to get link speed.

>>  For the moment the driver doesn't support second input port usage,
>> this is why there is no such second sink pad yet in the driver.
> 
> Could you add the second sink pad now, so that the uAPI remains the same
> when you add support for it? Nothing is connected to it but I don't think
> it's an issue.
> 
> ...
> 
>>>> +
>>>> +	sensor = mipid02_find_sensor(bridge);
>>>> +	if (!sensor)
>>>> +		goto error;
>>>> +
>>>> +	dev_dbg(&client->dev, "use sensor '%s'", sensor->name);
>>>> +	memset(&bridge->r, 0, sizeof(bridge->r));
>>>> +	/* build registers content */
>>>> +	code = mipid02_get_source_code(bridge, sensor);
>>>> +	ret |= mipid02_configure_from_rx(bridge, code, sensor);
>>>> +	ret |= mipid02_configure_from_tx(bridge);
>>>> +	ret |= mipid02_configure_from_code(bridge, code);
>>>> +
>>>> +	/* write mipi registers */
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_CLK_LANE_REG1,
>>>> +		bridge->r.clk_lane_reg1);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_CLK_LANE_REG3, CLK_MIPI_CSI);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_DATA_LANE0_REG1,
>>>> +		bridge->r.data_lane0_reg1);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_DATA_LANE0_REG2,
>>>> +		DATA_MIPI_CSI);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_DATA_LANE1_REG1,
>>>> +		bridge->r.data_lane1_reg1);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_DATA_LANE1_REG2,
>>>> +		DATA_MIPI_CSI);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_MODE_REG1,
>>>> +		MODE_NO_BYPASS | bridge->r.mode_reg1);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_MODE_REG2,
>>>> +		bridge->r.mode_reg2);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_DATA_ID_RREG,
>>>> +		bridge->r.data_id_rreg);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_DATA_SELECTION_CTRL,
>>>> +		SELECTION_MANUAL_DATA | SELECTION_MANUAL_WIDTH);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_PIX_WIDTH_CTRL,
>>>> +		bridge->r.pix_width_ctrl);
>>>> +	ret |= mipid02_write_reg(bridge, MIPID02_PIX_WIDTH_CTRL_EMB,
>>>> +		bridge->r.pix_width_ctrl_emb);
>>>
>>> Be careful with the error codes. ret will be returned by the s_stream
>>> callback below.
>>>
>>  I didn't understand your remark. Can you elaborate a little bit more ?
> 
> If the functions return different error codes, then ret possibly won't be a
> valid error code, or at least it's not going to be what it was intended to
> do. You'll need to stop when you encounter an error and then return it to
> the caller.
> 
> ...
> 
Ok
>>>> +static int mipid02_parse_tx_ep(struct mipid02_dev *bridge)
>>>> +{
>>>> +	struct i2c_client *client = bridge->i2c_client;
>>>> +	struct v4l2_fwnode_endpoint ep;
>>>> +	struct device_node *ep_node;
>>>> +	int ret;
>>>> +
>>>> +	memset(&ep, 0, sizeof(ep));
>>>> +	ep.bus_type = V4L2_MBUS_PARALLEL;
>>>
>>> You can set the field in variable declaration, and omit memset. The same in
>>> the function above.
>>>
>> According to v4l2_fwnode_endpoint_parse() documentation:
>>  * This function parses the V4L2 fwnode endpoint specific parameters from the
>>  * firmware. The caller is responsible for assigning @vep.bus_type to a valid
>>  * media bus type. The caller may also set the default configuration for the
>>  * endpoint
>> It seems safer to clear ep else it may select unwanted default configuration
>> for the endpoint ?
> 
> By setting one of the fields in a struct in declaration, the rest will be
> zeroed by the compiler. That's from the C standard.
> 
Ok

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