Hi,
On 18/11/2025 16:50, Laurent Pinchart wrote:
> Hi Linus, Marek,
>
> Thank you for the patch.
>
> On Tue, Nov 18, 2025 at 03:36:03PM +0100, Linus Walleij wrote:
>> From: Marek Vasut <[email protected]>
>>
>> Introduce a variant of drm_atomic_helper_commit_modeset_enables()
>> which enables CRTC before encoder/bridge. This is needed on R-Car DU,
>> where the CRTC provides clock to LVDS and DSI, and has to be started
>> before a bridge may call .prepare , which may trigger e.g. DSI transfer.
>>
>> This specifically fixes the case where ILI9881C is connected to R-Car
>> DU DSI. The ILI9881C panel driver does DSI command transfer in its
>> struct drm_panel_funcs .prepare function, which is currently called
>> before R-Car DU rcar_du_crtc_atomic_enable() rcar_mipi_dsi_pclk_enable()
>> and the DSI command transfer times out.
>>
>> Fix this by restoring the enable ordering introduced in commit
>> c9b1150a68d9 ("drm/atomic-helper: Re-order bridge chain pre-enable
>> and post-disable"), to enable CRTC early.
>
> This will need to be tested on Gen3 and Gen4 hardware, with different
> types of output in addition to DSI. Unfortunately you're catching me at
> a bad time as I'm about to board a plane and won't have access to test
> hardware for a month :-/ We'll need volunteers.
I can do some tests on my whitehawk. But I'm not too worried, this is
just restoring the order we had earlier.
Tomi
>> Fixes: c9b1150a68d9 ("drm/atomic-helper: Re-order bridge chain pre-enable
>> and post-disable")
>> Signed-off-by: Marek Vasut <[email protected]>
>> ---
>> drivers/gpu/drm/drm_atomic_helper.c | 24 ++++++++++++++++++++++++
>> drivers/gpu/drm/renesas/rcar-du/rcar_du_kms.c | 2 +-
>> include/drm/drm_atomic_helper.h | 2 ++
>> 3 files changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c
>> b/drivers/gpu/drm/drm_atomic_helper.c
>> index d5ebe6ea0acb..f03b93c72b8f 100644
>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> @@ -1692,6 +1692,30 @@ void drm_atomic_helper_commit_modeset_enables(struct
>> drm_device *dev,
>> }
>> EXPORT_SYMBOL(drm_atomic_helper_commit_modeset_enables);
>>
>> +/**
>> + * drm_atomic_helper_commit_modeset_enables_crtc_early - modeset commit to
>> enable outputs, start CRTC early
>> + * @dev: DRM device
>> + * @state: atomic state object being committed
>> + *
>> + * This function is a variant of drm_atomic_helper_commit_modeset_enables()
>> + * which enables CRTC before encoder/bridge. This is needed on R-Car DU,
>> + * where the CRTC provides clock to LVDS and DSI, and has to be started
>> + * before a bridge may call .prepare , which may trigger e.g. DSI transfer.
>> + */
>> +void
>> +drm_atomic_helper_commit_modeset_enables_crtc_early(struct drm_device *dev,
>> + struct drm_atomic_state
>> *state)
>> +{
>> + crtc_enable(dev, state);
>> +
>> + encoder_bridge_pre_enable(dev, state);
>> +
>> + encoder_bridge_enable(dev, state);
>> +
>> + drm_atomic_helper_commit_writebacks(dev, state);
>> +}
>> +EXPORT_SYMBOL(drm_atomic_helper_commit_modeset_enables_crtc_early);
>> +
>> /*
>> * For atomic updates which touch just a single CRTC, calculate the time of
>> the
>> * next vblank, and inform all the fences of the deadline.
>> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_du_kms.c
>> b/drivers/gpu/drm/renesas/rcar-du/rcar_du_kms.c
>> index 216219accfd9..b2403be4436b 100644
>> --- a/drivers/gpu/drm/renesas/rcar-du/rcar_du_kms.c
>> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_du_kms.c
>> @@ -544,7 +544,7 @@ static void rcar_du_atomic_commit_tail(struct
>> drm_atomic_state *old_state)
>> drm_atomic_helper_commit_modeset_disables(dev, old_state);
>> drm_atomic_helper_commit_planes(dev, old_state,
>> DRM_PLANE_COMMIT_ACTIVE_ONLY);
>> - drm_atomic_helper_commit_modeset_enables(dev, old_state);
>> + drm_atomic_helper_commit_modeset_enables_crtc_early(dev, old_state);
>>
>> drm_atomic_helper_commit_hw_done(old_state);
>> drm_atomic_helper_wait_for_flip_done(dev, old_state);
>> diff --git a/include/drm/drm_atomic_helper.h
>> b/include/drm/drm_atomic_helper.h
>> index 53382fe93537..d7fb473db343 100644
>> --- a/include/drm/drm_atomic_helper.h
>> +++ b/include/drm/drm_atomic_helper.h
>> @@ -93,6 +93,8 @@ void drm_atomic_helper_commit_modeset_disables(struct
>> drm_device *dev,
>> struct drm_atomic_state *state);
>> void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>> struct drm_atomic_state *old_state);
>> +void drm_atomic_helper_commit_modeset_enables_crtc_early(struct drm_device
>> *dev,
>> + struct
>> drm_atomic_state *old_state);
>>
>> int drm_atomic_helper_prepare_planes(struct drm_device *dev,
>> struct drm_atomic_state *state);
>
