On Wed, 11 Jan 2023, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> Hi
>
> Am 07.12.22 um 17:07 schrieb Maxime Ripard:
>> None of our wrappers around container_of to access our objects from the
>> DRM object pointer actually modify the latter.
>>
>> Let's make them const.
>>
>> Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>
>
> Personally, I wouldn't take this patch as it does an implicit const cast
> on the pointer.
>
> For const correctness, it seems better to add new helpers that keep the
> const. Those could be use in places where the caller is not allowed to
> modify the state (i.e., atomic_update, et al).
>
> Something like this:
>
> const struct vc4_hdmi *
> const_connector_to_vc4_hdmi(const struct drm_connector *connector)
> {
> return container_of(connector, const struct vc4_hdmi,
> connector);
> }
See container_of_const().
BR,
Jani.
>
> Best regards
> Thomas
>
>> ---
>> drivers/gpu/drm/vc4/vc4_hdmi.h | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
>> index dc3ccd8002a0..023ea64ef006 100644
>> --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
>> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
>> @@ -224,13 +224,13 @@ struct vc4_hdmi {
>> };
>>
>> static inline struct vc4_hdmi *
>> -connector_to_vc4_hdmi(struct drm_connector *connector)
>> +connector_to_vc4_hdmi(const struct drm_connector *connector)
>> {
>> return container_of(connector, struct vc4_hdmi, connector);
>> }
>>
>> static inline struct vc4_hdmi *
>> -encoder_to_vc4_hdmi(struct drm_encoder *encoder)
>> +encoder_to_vc4_hdmi(const struct drm_encoder *encoder)
>> {
>> struct vc4_encoder *_encoder = to_vc4_encoder(encoder);
>> return container_of(_encoder, struct vc4_hdmi, encoder);
>> @@ -244,7 +244,7 @@ struct vc4_hdmi_connector_state {
>> };
>>
>> static inline struct vc4_hdmi_connector_state *
>> -conn_state_to_vc4_hdmi_conn_state(struct drm_connector_state *conn_state)
>> +conn_state_to_vc4_hdmi_conn_state(const struct drm_connector_state *conn_state)
>> {
>> return container_of(conn_state, struct vc4_hdmi_connector_state, base);
>> }
>>
--
Jani Nikula, Intel Open Source Graphics Center
