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Subject: Re: [PATCH v4 15/15] ipu3-cio2: Add cio2-bridge to ipu3-cio2 driver
To:     kieran.bingham@ideasonboard.com, linux-kernel@vger.kernel.org,
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From:   Daniel Scally <djrscally@gmail.com>
Message-ID: <03dc26d0-39d3-174d-f269-426dbc38e62e@gmail.com>
Date:   Mon, 4 Jan 2021 22:02:59 +0000
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Hi Kieran

On 04/01/2021 16:13, Kieran Bingham wrote:
> Hi Dan,
> 
> On 04/01/2021 15:31, Daniel Scally wrote:
>> Hi Kieran
>>
>> On 04/01/2021 15:13, Kieran Bingham wrote:
>>> Hi Dan,
>>>
>>> On 04/01/2021 13:55, Daniel Scally wrote:
>>>> Hi Kieran
>>>>
>>>> On 04/01/2021 13:35, Kieran Bingham wrote:
>>>>>> +/*
>>>>>> + * Extend this array with ACPI Hardware IDs of devices known to be working
>>>>>> + * plus the number of link-frequencies expected by their drivers, along with
>>>>>> + * the frequency values in hertz. This is somewhat opportunistic way of adding
>>>>>> + * support for this for now in the hopes of a better source for the information
>>>>>> + * (possibly some encoded value in the SSDB buffer that we're unaware of)
>>>>>> + * becoming apparent in the future.
>>>>>> + *
>>>>>> + * Do not add an entry for a sensor that is not actually supported.
>>>>>> + */
>>>>>> +static const struct cio2_sensor_config cio2_supported_sensors[] = {
>>>>>> +	CIO2_SENSOR_CONFIG("INT33BE", 0),
>>>>>> +	CIO2_SENSOR_CONFIG("OVTI2680", 0),
>>>>> I don't know if these are expressed anywhere else but would it be
>>>>> helpful to add a comment, or indicator as to what the actual sensor is
>>>>> that is represented by this HID?
>>>>>
>>>>> I can make an assumption about what an OVTI2680 might be, but the
>>>>> INT33BE is quite opaque. It's not clear what support that adds.
>>>>>
>>>>> Unless no one cares what the sensor is that is, but I would anticipate
>>>>> anyone looking here to add a new sensor might want to investigate what
>>>>> was already in the table?
>>>> Yeah good point. I'll probably alternate comment and entry then, like:
>>>>
>>>>
>>>> +static const struct cio2_sensor_config cio2_supported_sensors[] = {
>>>> +	/* Sensor OVTI5693 */
>>>> +	CIO2_SENSOR_CONFIG("INT33BE", 0),
>>>> +	/* Sensor OVTI2680 */
>>>> +	CIO2_SENSOR_CONFIG("OVTI2680", 0),
>>>>
>>>> As an inline comment won't fit for the sensors that we know link-frequencies for. That sound ok?
>>> I might put the whole vendor name in, and no need to prefix 'Sensor' IMO.
>>>
>>> +	/* Omnivision OV5693 */
>>> +	CIO2_SENSOR_CONFIG("INT33BE", 0),
>>> +	/* Omnivision OV2680 */
>>> +	CIO2_SENSOR_CONFIG("OVTI2680", 0),
>>>
>>> but otherwise, yes a comment the line before works for me, as you are
>>> right - at the end would not be practical.
>> Works for me
>>>>>> +static void cio2_bridge_create_fwnode_properties(
>>>>>> +	struct cio2_sensor *sensor,
>>>>>> +	const struct cio2_sensor_config *cfg)
>>>>>> +{
>>>>>> +	unsigned int i;
>>>>>> +
>>>>>> +	sensor->prop_names = prop_names;
>>>>>> +
>>>>>> +	for (i = 0; i < CIO2_MAX_LANES; i++)
>>>>>> +		sensor->data_lanes[i] = i + 1;
>>>>> Does something support lane swapping somewhere?
>>>>> I assume this is just mapping each lane directly through.
>>>> I think Sakari said remapping isn't supported in the CIO2 - so yeah this
>>>> is just mapping them directly
>>> So is this needed? Or is it some future compatibility thing?
>>>
>>> I haven't seen where it's used yet, but I'm not too worried about it
>>> though, just not sure what value an array of [1, 2, 3, 4] gives if it's
>>> constant...
>>
>> The endpoints need to have the data-lanes property which passes an array
>> of data lanes, but there may well be a better way of doing this. I'm
>> just using the lanes member of the ssdb data structure to tell the
>> property how many members of the array to look at:
>>
>>
>> +    sensor->cio2_properties[0] = PROPERTY_ENTRY_U32_ARRAY_LEN(
>> +                    sensor->prop_names.data_lanes,
>> +                    sensor->data_lanes,
>> +                    sensor->ssdb.lanes);
>>
>>
>> So if sensor->ssdb.lanes is 2, even though it's passed a pointer to the
>> first member of an array of 4 members, the size calculation of that
>> macro limits it to just those in use. I.E. if sensor->ssdb.lanes is 2
>> then the property will be given the size 2 * sizeof(u32), and so when
>> its parsed only [1, 2] will be read.
> 
> 
> Aha, I see, ok - so we are populating an array of [1, 2, 3, 4] for each
> sensor that we add.
> 
> What about creating the data_lanes once as a const static array and
> mapping to that?
> 
> /*
>  * Map the lane arrangement, which is fixed for the IPU3.
>  */
> static const int data_lanes[CIO2_MAX_LANES] = { 1, 2, 3, 4 };


Can't do exactly this; the bridge needs to store everything on heap
incase the module is unloaded, but I could move the data_lanes array to
the struct cio2_bridge instead of against each sensor and then we're
only doing it once.

> ...
> 
>    sensor->cio2_properties[0] = PROPERTY_ENTRY_U32_ARRAY_LEN(
>                     sensor->prop_names.data_lanes,
>                     data_lanes,
>                     sensor->ssdb.lanes);
> ...
> 
> Then we don't need the loop to populate the array for each sensor
> anymore, or the data_lanes in the sensor struct?
>