Re: [PATCH v3 01/22] drm: Include ddc adapter pointer in struct drm_connector

Thomas Zimmermann
2019-07-01T14:41:09Z

Hi

Am 01.07.19 um 15:27 schrieb Andrzej Pietrasiewicz:
> Hi Thomas,
>
> Thank you for your comments. Please see inline.
>
> W dniu 30.06.2019 o 10:12, Thomas Zimmermann pisze:
>> Hi
>>
>> I like the idea, but would prefer a more structured approach.
>>
>> Setting connector->ddc before calling drm_sysfs_connector_add() seems
>> error prone. The dependency is not really clear from the code or
>> interfaces.
>>
>> The other thing is that drivers I mostly work on, ast and mgag200, have
>> code like this:
>>
>>    struct ast_i2c_chan {
>>     struct i2c_adapter adapter;
>>     struct drm_device *dev;
>>     struct i2c_algo_bit_data bit;
>>    };
>>
>>    struct ast_connector {
>>     struct drm_connector base;
>>     struct ast_i2c_chan *i2c;
>>    };
>>
>> It already encodes the connection between connector and ddc adapter.
>>
>> I suggest to introduce struct drm_i2c_adapter
>>
>>    struct drm_i2c_adapter {
>>     struct i2c_adapter base;
>>     struct drm_connector *connector;
>>    };
>>
>> and convert drivers over to it. Ast would look like this:
>>
>>    struct ast_i2c_chan {
>>     struct drm_i2c_adapter adapter;
>>     struct i2c_algo_bit_data bit;
>>    };
>>
>
> There are few flavors of these drivers. In some of them
> the i2c_adapter for ddc is allocated and initialized by
> the driver, which must provide a place in memory to hold
> the adapter. ast is an example of this approach.
>
> But there are others, such as for example exynos_hdmi.c.
> It gets its ddc adapter with of_find_i2c_adapter_by_node()
> and merely stores a pointer to it, while not managing the
> memory needed to hold the i2c_adapter.

I see.

> Do you have any idea how to accommodate these various
> flavors of drivers in the scheme you propose?

Something like

struct drm_i2c_adapter {
struct i2c_adapter *adapter;
struct drm_connector *connector;
};

with adapter either being allocated dynamically or acquired via
of_find_i2c_adapter_by_node(); with separate init and finish functions
for each variant. But it looks like over-abstraction to me. Without
prototyping the idea, I cannot say if it's worth the effort.

For something more simple, maybe just have a function to attach an i2c
adapter to a connector:

drm_connector_attach_i2c_adapter(connector, i2c_adapter)

which sets the connector's ddc pointer and creates the sysfs entry if
the connector's entry is already present.

Best regards
Thomas

> Andrzej
>
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
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