[PATCH v2] drm/tidss: dispc: Rewrite naive plane positioning code

[Jyri Sarha]

On 12/02/2020 15:59, Jyri Sarha wrote:
> The old implementation of placing planes on the CRTC while configuring
> the planes was naive and relied on the order in which the planes were
> configured, enabled, and disabled. The situation where a plane's zpos
> was changed on the fly was completely broken. The usual symptoms of
> this problem was scrambled display and a flood of sync lost errors,
> when a plane was active in two layers at the same time, or a missing
> plane, in case when a layer was accidentally disabled.
> 
> The rewrite takes a more straight forward approach when HW is
> concerned. The plane positioning registers are in the CRTC (actually
> OVR) register space and it is more natural to configure them in one go
> while configuring the CRTC. To do this we need to make sure we have
> all the planes on updated CRTCs in the new atomic state to be
> committed. This is done by calling drm_atomic_add_affected_planes() in
> crtc_atomic_check().
> 
> Signed-off-by: Jyri Sarha <jsarha at ti.com>
> ---
>  drivers/gpu/drm/tidss/tidss_crtc.c  | 55 ++++++++++++++++++++++++++++-
>  drivers/gpu/drm/tidss/tidss_dispc.c | 55 +++++++++++------------------
>  drivers/gpu/drm/tidss/tidss_dispc.h |  5 +++
>  3 files changed, 79 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_crtc.c b/drivers/gpu/drm/tidss/tidss_crtc.c
> index 032c31ee2820..f7c5fd1094a8 100644
> --- a/drivers/gpu/drm/tidss/tidss_crtc.c
> +++ b/drivers/gpu/drm/tidss/tidss_crtc.c
...
> @@ -108,7 +110,54 @@ static int tidss_crtc_atomic_check(struct drm_crtc *crtc,
>  		return -EINVAL;
>  	}
>  
> -	return dispc_vp_bus_check(dispc, hw_videoport, state);
> +	ret = dispc_vp_bus_check(dispc, hw_videoport, state);
> +	if (ret)
> +		return ret;
> +
> +	/* Add unchanged planes on this crtc to state for zpos update. */
> +	return drm_atomic_add_affected_planes(state->state, crtc);

Is this a correct way to use drm_atomic_add_affected_planes()?

I saw that some other drivers implement their own mode_config
atomic_check() and have this call there in
for_each_new_crtc_in_state()-loop, but I thought it should be fine to
call it in crtc_atomic_check().

BR,
Jyri

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