Re: [PATCH v7 06/15] drm/imx: dc-crtc: Disable at boot

[Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>]

On Mon, Oct 26, 2026 at 06:05:11PM +0800, Liu Ying wrote:
> CRTC(s) could still be running after the DRM device is unplugged by
> calling drm_dev_unplug(), because the CRTC disablement logic is
> protected and bypassed by the drm_dev_enter()/drm_dev_exit() pair.
> Hence, Pixel Engine's AXI clock use count(managed by Pixel Engine
> driver's runtime PM) and pixel clock use count could be inbalanced
> after removing and re-installing the driver module.  To fix this,
> add a helper dc_crtc_disable_at_boot() and call it to properly
> disable all CRTCs before advertising DRM device to user-space by
> calling drm_dev_register().
> 
> Fixes: 711a3b878366 ("drm/imx: Add i.MX8qxp Display Controller KMS")
> Reviewed-by: Frank Li <Frank.Li@nxp.com>
> Signed-off-by: Liu Ying <victor.liu@nxp.com>
> --
> v7:
> - Check CRTC status to ensure that clocks were enabled by a previous boot
>   before disabling them in dc_crtc_disable_at_boot().  (Sashiko AI bot)
> - Modify debug message in dc_crtc_disable_at_boot().
> 
> v6:
> - Rebase onto the latest drm-misc-next and resolve conflicts.
> 
> v3:
> - Collect Frank's R-b tag.
> ---
>  drivers/gpu/drm/imx/dc/dc-crtc.c | 67 ++++++++++++++++++++++++++++++++++------
>  drivers/gpu/drm/imx/dc/dc-drv.c  |  5 +++
>  drivers/gpu/drm/imx/dc/dc-drv.h  |  3 ++
>  3 files changed, 65 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/imx/dc/dc-crtc.c b/drivers/gpu/drm/imx/dc/dc-crtc.c
> index 0d64186a9901..c7dbe5f500b4 100644
> --- a/drivers/gpu/drm/imx/dc/dc-crtc.c
> +++ b/drivers/gpu/drm/imx/dc/dc-crtc.c
> @@ -227,6 +227,7 @@ dc_crtc_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_commit *state)
>  	struct drm_crtc_state *new_crtc_state =
>  				drm_atomic_get_new_crtc_state(state, crtc);
>  	struct drm_display_mode *adj = &new_crtc_state->adjusted_mode;
> +	struct dc_drm_device *dc_drm = to_dc_drm_device(crtc->dev);
>  	struct dc_crtc *dc_crtc = to_dc_crtc(crtc);
>  	enum dc_link_id cf_link;
>  	int idx, ret;
> @@ -287,29 +288,37 @@ dc_crtc_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_commit *state)
>  
>  	DC_CRTC_CHECK_FRAMEGEN_FIFO(dc_crtc->fg);
>  
> +	dc_drv_set_crtc_enable(dc_drm, drm_crtc_index(crtc));
> +
>  	drm_dev_exit(idx);
>  
>  out:
>  	dc_crtc_queue_state_event(new_crtc_state);
>  }
>  
> -static void
> -dc_crtc_atomic_disable(struct drm_crtc *crtc, struct drm_atomic_commit *state)
> +static inline void __dc_crtc_disable_fg(struct drm_crtc *crtc)
>  {
> -	struct drm_crtc_state *new_crtc_state =
> -				drm_atomic_get_new_crtc_state(state, crtc);
> -	struct dc_drm_device *dc_drm = to_dc_drm_device(crtc->dev);
>  	struct dc_crtc *dc_crtc = to_dc_crtc(crtc);
> -	int idx;
> -
> -	if (!drm_dev_enter(crtc->dev, &idx))
> -		goto out;
>  
>  	enable_irq(dc_crtc->irq_dec_seqcomplete);
>  	dc_fg_disable(dc_crtc->fg);
>  	DC_CRTC_WAIT_FOR_COMPLETION_TIMEOUT(dec_seqcomplete_done);
>  	disable_irq(dc_crtc->irq_dec_seqcomplete);
> +}
>  
> +static void
> +dc_crtc_atomic_disable(struct drm_crtc *crtc, struct drm_atomic_commit *state)
> +{
> +	struct drm_crtc_state *new_crtc_state =
> +				drm_atomic_get_new_crtc_state(state, crtc);
> +	struct dc_drm_device *dc_drm = to_dc_drm_device(crtc->dev);
> +	struct dc_crtc *dc_crtc = to_dc_crtc(crtc);
> +	int idx;
> +
> +	if (!drm_dev_enter(crtc->dev, &idx))
> +		goto out;
> +
> +	__dc_crtc_disable_fg(crtc);
>  	dc_fg_disable_clock(dc_crtc->fg);
>  
>  	/* request pixel engine power-off as plane is off too */
> @@ -318,8 +327,9 @@ dc_crtc_atomic_disable(struct drm_crtc *crtc, struct drm_atomic_commit *state)
>  	/* request display engine power-off when CRTC is disabled */
>  	pm_runtime_put(dc_crtc->de->dev);
>  
> -	drm_dev_exit(idx);
> +	dc_drv_set_crtc_disable(dc_drm, drm_crtc_index(crtc));
>  
> +	drm_dev_exit(idx);
>  out:
>  	drm_crtc_vblank_off(crtc);
>  
> @@ -331,6 +341,43 @@ dc_crtc_atomic_disable(struct drm_crtc *crtc, struct drm_atomic_commit *state)
>  	spin_unlock_irq(&crtc->dev->event_lock);
>  }
>  
> +void dc_crtc_disable_at_boot(struct drm_crtc *crtc)

Shouldn't this function return int in order to propagate a potential error to
dc_drm_bind()? For example, if pm_runtime_resume_and_get() fails, or frame
index isn't moving, wouldn't it be better for dc_drm_bind() to fail as well?

-- 
Thanks,
Laurentiu