Hi Maxime,
Thank you for reviewing the patches!
On 16/05/24 13:52, Maxime Ripard wrote:
> On Sat, May 11, 2024 at 09:00:50PM +0530, Aradhya Bhatia wrote:
>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>> index 4baca0d9107b..40f93230abb2 100644
>> --- a/include/drm/drm_bridge.h
>> +++ b/include/drm/drm_bridge.h
>> @@ -206,6 +206,20 @@ struct drm_bridge_funcs {
>> */
>> void (*post_disable)(struct drm_bridge *bridge);
>>
>> + /**
>> + * @late_disable:
>> + *
>> + * This callback should disable the bridge. It is called right after the
>> + * preceding element in the display pipe is disabled. If the preceding
>> + * element is a bridge this means it's called after that bridge's
>> + * @atomic_post_disable. If the preceding element is a &drm_crtc it's
>> + * called right after the crtc's &drm_crtc_helper_funcs.atomic_disable
>> + * hook.
>> + *
>> + * The @late_disable callback is optional.
>> + */
>> + void (*late_disable)(struct drm_bridge *bridge);
>> +
>> /**
>> * @mode_set:
>> *
>> @@ -235,6 +249,26 @@ struct drm_bridge_funcs {
>> void (*mode_set)(struct drm_bridge *bridge,
>> const struct drm_display_mode *mode,
>> const struct drm_display_mode *adjusted_mode);
>> +
>> + /**
>> + * @early_enable:
>> + *
>> + * This callback should enable the bridge. It is called right before
>> + * the preceding element in the display pipe is enabled. If the
>> + * preceding element is a bridge this means it's called before that
>> + * bridge's @early_enable. If the preceding element is a &drm_crtc it's
>> + * called right before the crtc's &drm_crtc_helper_funcs.atomic_enable
>> + * hook.
>> + *
>> + * The display pipe (i.e. clocks and timing signals) feeding this bridge
>> + * will not yet be running when this callback is called. The bridge can
>> + * enable the display link feeding the next bridge in the chain (if
>> + * there is one) when this callback is called.
>> + *
>> + * The @early_enable callback is optional.
>> + */
>> + void (*early_enable)(struct drm_bridge *bridge);
>> +
>
> You don't need the legacy option here, just go straight for the atomic one.
Got it! I can remove these in v2.
>
>> /**
>> * @pre_enable:
>> *
>> @@ -285,6 +319,26 @@ struct drm_bridge_funcs {
>> */
>> void (*enable)(struct drm_bridge *bridge);
>>
>> + /**
>> + * @atomic_early_enable:
>> + *
>> + * This callback should enable the bridge. It is called right before
>> + * the preceding element in the display pipe is enabled. If the
>> + * preceding element is a bridge this means it's called before that
>> + * bridge's @atomic_early_enable. If the preceding element is a
>> + * &drm_crtc it's called right before the crtc's
>> + * &drm_crtc_helper_funcs.atomic_enable hook.
>> + *
>> + * The display pipe (i.e. clocks and timing signals) feeding this bridge
>> + * will not yet be running when this callback is called. The bridge can
>> + * enable the display link feeding the next bridge in the chain (if
>> + * there is one) when this callback is called.
>> + *
>> + * The @early_enable callback is optional.
>> + */
>> + void (*atomic_early_enable)(struct drm_bridge *bridge,
>> + struct drm_bridge_state *old_bridge_state);
>> +
>> /**
>> * @atomic_pre_enable:
>> *
>> @@ -361,6 +415,21 @@ struct drm_bridge_funcs {
>> void (*atomic_post_disable)(struct drm_bridge *bridge,
>> struct drm_bridge_state *old_bridge_state);
>>
>> + /**
>> + * @atomic_late_disable:
>> + *
>> + * This callback should disable the bridge. It is called right after the
>> + * preceding element in the display pipe is disabled. If the preceding
>> + * element is a bridge this means it's called after that bridge's
>> + * @atomic_late_disable. If the preceding element is a &drm_crtc it's
>> + * called right after the crtc's &drm_crtc_helper_funcs.atomic_disable
>> + * hook.
>> + *
>> + * The @atomic_late_disable callback is optional.
>> + */
>> + void (*atomic_late_disable)(struct drm_bridge *bridge,
>> + struct drm_bridge_state *old_bridge_state);
>> +
>
> But more importantly, I don't quite get the use case you're trying to
> solve here.
>
> If I got the rest of your series, the Cadence DSI bridge needs to be
> powered up before its source is started. You can't use atomic_enable or
> atomic_pre_enable because it would start the source before the DSI
> bridge. Is that correct?
>
That's right. I cannot use bridge_atomic_pre_enable /
bridge_atomic_enable here. But that's because my source is CRTC, which
gets enabled via crtc_atomic_enable.
> If it is, then how is it different from what
> drm_atomic_bridge_chain_pre_enable is doing? The assumption there is
> that it starts enabling bridges last to first, to it should be enabled
> before anything starts.
>
> The whole bridge enabling order code starts to be a bit of a mess, so it
> would be great if you could list all the order variations we have
> currently, and why none work for cdns-dsi.
>
Of course! I can elaborate on the order.
Without my patches (and given there isn't any bridge setting the
"pre_enable_prev_first" flag) the order of enable for any single display
chain, looks like this -
crtc_enable
bridge[n]_pre_enable
---
bridge[1]_pre_enable
encoder_enable
bridge[1]_enable
---
bridge[n]_enable
The tidss enables at the crtc_enable level, and hence is the first
entity with stream on. cdns-dsi doesn't stand a chance with
bridge_atmoic_pre_enable / bridge_atmoic_enable hooks. And there is no
bridge call happening before crtc currently.
That's where the early_enable APIs come into picture. They are being
called before the crtc is even enabled, helping cdns-dsi to be enabled
before tidss. The order then looks like -
bridge[1]_early_enable
---
bridge[n]_early_enable
crtc_enable
---
(the order is same from here on)
Regards
Aradhya
