Re: [Intel-gfx] [PATCH 2/3] drm: Create a drm_connector_helper_funcs hook for Adaptive Sync support

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 17 Mar 2020, Manasi Navare <manasi.d.navare@intel.com> wrote:
> This patch adds a hook in drm_connector_helper_funcs to get the
> support of the driver for adaptive sync functionality.
>
> This can be called in the connector probe helper function after
> the connector detect() and get_modes() hooks to also
> query the adaptive sync support of the driver.

I can obviously see that from the patch. But this does not explain at
all *why* we need another hook to begin with, and why it neeeds to be
called from ->fill_modes that is set to
drm_helper_probe_single_connector_modes().

> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/drm_probe_helper.c       |  4 ++++
>  include/drm/drm_modeset_helper_vtables.h | 16 ++++++++++++++++
>  2 files changed, 20 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 576b4b7dcd89..4403817bfb02 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -482,6 +482,10 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  
>  	count = (*connector_funcs->get_modes)(connector);
>  
> +	/* Get the Adaptive Sync Support if helper exists */
> +	if (*connector_funcs->get_adaptive_sync_support)
> +		(**connector_funcs->get_adaptive_sync_support)(connector);
> +

This is in the middle of a sequence figuring out the modes. First
->get_modes, then fallback to other mechanisms. Certainly we don't want
to do something else in the middle.

>  	/*
>  	 * Fallback for when DDC probe failed in drm_get_edid() and thus skipped
>  	 * override/firmware EDID.
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index 7c20b1c8b6a7..0b203fdd25df 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -1079,6 +1079,22 @@ struct drm_connector_helper_funcs {
>  				     struct drm_writeback_job *job);
>  	void (*cleanup_writeback_job)(struct drm_writeback_connector *connector,
>  				      struct drm_writeback_job *job);
> +
> +	/**
> +	 * @get_adaptive_sync_support:
> +	 *
> +	 * This hook is used by the probe helper to get the driver's support
> +	 * for adaptive sync or variable refresh rate.
> +	 * This is called from drm_helper_probe_single_connector_modes()
> +	 * This is called after the @get_modes hook so that the connector modes
> +	 * are already obtained and EDID is parsed to obtain the monitor
> +	 * range descriptor information.
> +	 *
> +	 * This hook is optional and defined only for the drivers and on
> +	 * connectors that advertise adaptive sync support.
> +	 *
> +	 */
> +	void (*get_adaptive_sync_support)(struct drm_connector *connector);
>  };
>  
>  /**

-- 
Jani Nikula, Intel Open Source Graphics Center
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