Re: [PATCH v3 1/2] drm/imx/lcdc: avoid duplicate clk_per enable

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 26.07.26 um 21:42 schrieb Ze Huang:
> The simple-KMS helper calls the pipe update after enabling the CRTC.
> On an enable commit, imx_lcdc_pipe_enable() already programs the
> mode and enables clk_per. The following pipe update sees the plane move
> from no CRTC to the active CRTC, treats it as a mode update, and calls
> imx_lcdc_update_hw_registers() again.
>
> That second call has no old CRTC state to disable clk_per first, but it
> enables clk_per again at the end. The disable path only drops one
> reference, leaving clk_per enabled after each on/off cycle.
>
> Skip the register update from the pipe update path when the CRTC already
> needs a modeset. The enable path has already programmed the hardware for
> that commit; keep the event handling in pipe update unchanged.
That seems reasonable. Once the driver uses regular DRM helpers instead 
of simple_kms, it can all be untangled and this test won't be necessary 
any longer.
> Fixes: c87e859cdeb5 ("drm/imx/lcdc: Implement DRM driver for imx25")
> Signed-off-by: Ze Huang <ze.huang@xxxxxxxxxxxxxxxx>
Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

> ---
>   drivers/gpu/drm/imx/lcdc/imx-lcdc.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/imx/lcdc/imx-lcdc.c 
> b/drivers/gpu/drm/imx/lcdc/imx-lcdc.c
> index f52832b43aca..81024f7d9e96 100644
> --- a/drivers/gpu/drm/imx/lcdc/imx-lcdc.c
> +++ b/drivers/gpu/drm/imx/lcdc/imx-lcdc.c
> @@ -311,7 +311,8 @@ static void imx_lcdc_pipe_update(struct 
> drm_simple_display_pipe *pipe,
>         else if (old_crtc != crtc)
>                 mode_changed = true;
>   
> -	imx_lcdc_update_hw_registers(pipe, old_state, mode_changed);
> +       if (!drm_atomic_crtc_needs_modeset(crtc->state))
> +               imx_lcdc_update_hw_registers(pipe, old_state, mode_changed);
>   
>   	if (event) {
>                 crtc->state->event = NULL;
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)