Re: [PATCH v3 06/26] drm/i915/writeback: Add function to get modes

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

On 3/25/2026 4:37 PM, Suraj Kandpal wrote:
> Add a function that get modes for writeback connector.
> Since we have a restriction on supporting only 3840x2160 60Hz modes
> at max we will create modes only up until that point.
> 
> Bspec: 49275
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>   drivers/gpu/drm/i915/display/intel_writeback.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_writeback.c b/drivers/gpu/drm/i915/display/intel_writeback.c
> index 73101ee17d74..852951933348 100644
> --- a/drivers/gpu/drm/i915/display/intel_writeback.c
> +++ b/drivers/gpu/drm/i915/display/intel_writeback.c
> @@ -10,6 +10,7 @@
>   #include <drm/drm_probe_helper.h>
>   #include <drm/drm_fourcc.h>
>   #include <drm/drm_encoder.h>
> +#include <drm/drm_edid.h>
>   
>   #include "intel_atomic.h"
>   #include "intel_connector.h"
> @@ -58,6 +59,11 @@ intel_writeback_connector_alloc(struct intel_connector *connector)
>   	return 0;
>   }
>   
> +static int intel_writeback_get_modes(struct drm_connector *connector)
> +{
> +	return drm_add_modes_noedid(connector, 3840, 2160);

This is based on drm_dmt_modes and the only 4k mode it lists is 
4096x2160 which means we are capped at 2560x1600. Therfore, we are 
missing out on the best mode our HW can support.

Perhaps we need something based on edid_cea_modes_1.

Also have we tested if all the modes we advertise work?

> +}
> +
>   static const struct drm_encoder_funcs drm_writeback_encoder_funcs = {
>   	.destroy = drm_encoder_cleanup,
>   };
> @@ -69,6 +75,7 @@ const struct drm_connector_funcs conn_funcs = {
>   };
>   
>   static const struct drm_connector_helper_funcs conn_helper_funcs = {
> +	.get_modes = intel_writeback_get_modes,
>   };
>   
>   int intel_writeback_init(struct intel_display *display)