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SubjectRe: [RFC PATCH 2/3] drm: bridge: panel: allow override of the bus format
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Hi Laurent,

Thanks for the feedback!

On 2018-03-20 14:56, Laurent Pinchart wrote:
> Hi Peter,
>
> Thank you for the patch.
>
> On Sunday, 18 March 2018 00:15:24 EET Peter Rosin wrote:
>> Useful if the bridge does some kind of conversion of the bus format.
>>
>> Signed-off-by: Peter Rosin <peda@axentia.se>
>> ---
>> drivers/gpu/drm/bridge/panel.c | 22 +++++++++++++++++++++-
>> include/drm/drm_bridge.h | 1 +
>> 2 files changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
>> index 6d99d4a3beb3..ccef0283ff41 100644
>> --- a/drivers/gpu/drm/bridge/panel.c
>> +++ b/drivers/gpu/drm/bridge/panel.c
>> @@ -22,6 +22,7 @@ struct panel_bridge {
>> struct drm_connector connector;
>> struct drm_panel *panel;
>> u32 connector_type;
>> + u32 bus_format;
>> };
>>
>> static inline struct panel_bridge *
>> @@ -40,8 +41,15 @@ static int panel_bridge_connector_get_modes(struct
>> drm_connector *connector) {
>> struct panel_bridge *panel_bridge =
>> drm_connector_to_panel_bridge(connector);
>> + int ret;
>> +
>> + ret = drm_panel_get_modes(panel_bridge->panel);
>> +
>> + if (panel_bridge->bus_format)
>> + drm_display_info_set_bus_formats(&connector->display_info,
>> + &panel_bridge->bus_format, 1);
>
> While I agree with the problem statement and, to some extent, the DT bindings,
> I don't think this is the right implementation. You've correctly noted that
> display controller shouldn't blindly use the formats reported by the panel
> through the connector formats, and that hacking the panel driver to override
> the formats isn't a good idea, so I wouldn't override the formats reported by
> the connector. I would instead extend the drm_bridge API to report formats at
> bridge inputs. This would be more generic and allow each bridge to configure
> itself according to the next bridge in the chain.
>
> I'm not sure whether this API extension should be in the form of a new bridge
> function, or if the formats should be stored in the drm_bridge structure
> directly as done for connectors in the display info structure. I'm tempted by
> the former, but I'm open to discussions.

Ok, I can look into that, but let me check if I got this right. From the very
little of the code that I have looked at, I have gathered that display
controllers handle bridges explicitly, right? If so, by extending the bridge
(with either a new function or new data) you impose changes to all display
controllers wanting to handle this new bridge input-format. If so, I assume
I can leave out the changes to all display controllers that I do not care
about. Correct?

Also, don't hold your breath waiting for a v2, but I'll try to get to it :-)

>> - return drm_panel_get_modes(panel_bridge->panel);
>> + return ret;
>> }
>>
>> static const struct drm_connector_helper_funcs
>> @@ -203,6 +211,18 @@ void drm_panel_bridge_remove(struct drm_bridge *bridge)
>> }
>> EXPORT_SYMBOL(drm_panel_bridge_remove);
>>
>> +void drm_panel_bridge_set_bus_format(struct drm_bridge *bridge, u32
>> bus_format) +{
>> + struct panel_bridge *panel_bridge;
>> +
>> + if (!bridge)
>> + return;
>> +
>> + panel_bridge = drm_bridge_to_panel_bridge(bridge);
>> + panel_bridge->bus_format = bus_format;
>> +}
>> +EXPORT_SYMBOL(drm_panel_bridge_set_bus_format);
>> +
>> static void devm_drm_panel_bridge_release(struct device *dev, void *res)
>> {
>> struct drm_bridge **bridge = res;
>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>> index 682d01ba920c..81903b92f187 100644
>> --- a/include/drm/drm_bridge.h
>> +++ b/include/drm/drm_bridge.h
>> @@ -268,6 +268,7 @@ void drm_bridge_enable(struct drm_bridge *bridge);
>> struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel,
>> u32 connector_type);
>> void drm_panel_bridge_remove(struct drm_bridge *bridge);
>> +void drm_panel_bridge_set_bus_format(struct drm_bridge *bridge, u32
>> bus_format);
>> struct drm_bridge *devm_drm_panel_bridge_add(struct device
>> *dev,
>> struct drm_panel *panel,
>> u32 connector_type);
>

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