Re: [PATCH v2 2/2] drm/komeda: Set display/writeback clone masks

[Liviu Dudau <liviu.dudau@arm.com>]

On Mon, Aug 03, 2026 at 03:21:22PM +0100, Raveendra Talabattula wrote:
> From: Vincenzo Frascino <vincenzo.frascino@arm.com>
> 
> Since commit 41b4b11da0215 ("drm: Add valid clones check"),
> all encoders attached to the same CRTC must advertise
> each other through possible_clones.
> 
> Komeda creates one writeback connector per CRTC. Allow the writeback
> encoder to be cloned only with encoders that can drive the same CRTC,
> and update those encoders reciprocally.
> 
> Do this when the writeback connector is created rather than modifying
> every encoder registered with the DRM device from komeda_kms_attach().
> This leaves encoders associated with other CRTCs untouched.

If you don't mind I will drop the paragraph above when I commit the patch
as it makes reference to code that has not been merged so likely
to create confusion. I think the comment in the code is sufficient.

With that,

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Will push this to drm-misc-next in the next couple of days.

Best regards,
Liviu

> 
> Signed-off-by: Asad Malik <asad.malik@arm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Co-developed-by: Raveendra Talabattula <raveendra.talabattula@arm.com>
> Signed-off-by: Raveendra Talabattula <raveendra.talabattula@arm.com>
> ---
>  .../arm/display/komeda/komeda_wb_connector.c  | 33 +++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c b/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c
> index 41cc3e080dc9..4872253a2449 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_wb_connector.c
> @@ -143,12 +143,17 @@ static int komeda_wb_connector_add(struct komeda_kms_dev *kms,
>  	struct komeda_wb_connector *kwb_conn;
>  	struct drm_writeback_connector *wb_conn;
>  	struct drm_display_info *info;
> +	struct drm_encoder *encoder;
> +	struct drm_encoder *wb_encoder;
>  	u32 *formats, n_formats = 0;
> +	u32 crtc_mask;
>  	int err;
>  
>  	if (!kcrtc->master->wb_layer)
>  		return 0;
>  
> +	crtc_mask = drm_crtc_mask(&kcrtc->base);
> +
>  	kwb_conn = kzalloc_obj(*kwb_conn);
>  	if (!kwb_conn)
>  		return -ENOMEM;
> @@ -176,6 +181,34 @@ static int komeda_wb_connector_add(struct komeda_kms_dev *kms,
>  		return err;
>  	}
>  
> +	wb_encoder = &wb_conn->encoder;
> +
> +	/*
> +	 * The writeback connector is associated with a single CRTC. Make its
> +	 * encoder clone-compatible only with encoders that can drive that CRTC.
> +	 *
> +	 * possible_clones must contain the encoder's own bit whenever it is
> +	 * non-zero. Add both the encoder itself and the writeback encoder when
> +	 * updating the reciprocal clone relationship.
> +	 */
> +	wb_encoder->possible_clones = drm_encoder_mask(wb_encoder);
> +
> +	drm_for_each_encoder(encoder, &kms->base) {
> +		u32 encoder_mask;
> +
> +		if (encoder == wb_encoder)
> +			continue;
> +
> +		if (!(encoder->possible_crtcs & crtc_mask))
> +			continue;
> +
> +		encoder_mask = drm_encoder_mask(encoder);
> +
> +		wb_encoder->possible_clones |= encoder_mask;
> +		encoder->possible_clones |= encoder_mask |
> +					    drm_encoder_mask(wb_encoder);
> +	}
> +
>  	drm_connector_helper_add(&wb_conn->base, &komeda_wb_conn_helper_funcs);
>  
>  	info = &kwb_conn->base.base.display_info;
> -- 
> 2.43.0
> 

-- 
====================
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| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
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