linux-kernel - Re: [PATCH 4/6] drm: vkms: Add fb information to `vkms_writeback

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Date:   Mon, 18 Oct 2021 12:10:34 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Igor Matheus Andrade Torrente <igormtorrente@...il.com>,
        rodrigosiqueiramelo@...il.com, melissa.srw@...il.com
Cc:     hamohammed.sa@...il.com, daniel@...ll.ch, airlied@...ux.ie,
        contact@...rsion.fr, leandro.ribeiro@...labora.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        lkcamp@...ts.libreplanetbr.org
Subject: Re: [PATCH 4/6] drm: vkms: Add fb information to `vkms_writeback_job`

Hi

Am 05.10.21 um 22:16 schrieb Igor Matheus Andrade Torrente:
> This commit is the groundwork to introduce new formats to the planes and
> writeback buffer. As part of it, a new buffer metadata field is added to
> `vkms_writeback_job`, this metadata is represented by the `vkms_composer`
> struct.
> 
> This will allow us, in the future, to have different compositing and wb
> format types.
> 
> Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@...il.com>
> ---
>   drivers/gpu/drm/vkms/vkms_drv.h       | 10 +++++-----
>   drivers/gpu/drm/vkms/vkms_writeback.c | 16 +++++++++++++---
>   2 files changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 64e62993b06f..d62f8ebd454b 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -20,11 +20,6 @@
>   #define XRES_MAX  8192
>   #define YRES_MAX  8192
>   
> -struct vkms_writeback_job {
> -	struct dma_buf_map map[DRM_FORMAT_MAX_PLANES];
> -	struct dma_buf_map data[DRM_FORMAT_MAX_PLANES];
> -};
> -
>   struct vkms_composer {
>   	struct drm_framebuffer fb;
>   	struct drm_rect src, dst;
> @@ -34,6 +29,11 @@ struct vkms_composer {
>   	unsigned int cpp;
>   };
>   
> +struct vkms_writeback_job {
> +	struct dma_buf_map data[DRM_FORMAT_MAX_PLANES];
> +	struct vkms_composer composer;
> +};
> +
>   /**
>    * vkms_plane_state - Driver specific plane state
>    * @base: base plane state
> diff --git a/drivers/gpu/drm/vkms/vkms_writeback.c b/drivers/gpu/drm/vkms/vkms_writeback.c
> index 8694227f555f..5a3e12f105dc 100644
> --- a/drivers/gpu/drm/vkms/vkms_writeback.c
> +++ b/drivers/gpu/drm/vkms/vkms_writeback.c
> @@ -75,7 +75,7 @@ static int vkms_wb_prepare_job(struct drm_writeback_connector *wb_connector,
>   	if (!vkmsjob)
>   		return -ENOMEM;
>   
> -	ret = drm_gem_fb_vmap(job->fb, vkmsjob->map, vkmsjob->data);
> +	ret = drm_gem_fb_vmap(job->fb, vkmsjob->composer.map, vkmsjob->data);
>   	if (ret) {
>   		DRM_ERROR("vmap failed: %d\n", ret);
>   		goto err_kfree;
> @@ -99,7 +99,7 @@ static void vkms_wb_cleanup_job(struct drm_writeback_connector *connector,
>   	if (!job->fb)
>   		return;
>   
> -	drm_gem_fb_vunmap(job->fb, vkmsjob->map);
> +	drm_gem_fb_vunmap(job->fb, vkmsjob->composer.map);
>   
>   	vkmsdev = drm_device_to_vkms_device(job->fb->dev);
>   	vkms_set_composer(&vkmsdev->output, false);
> @@ -116,14 +116,24 @@ static void vkms_wb_atomic_commit(struct drm_connector *conn,
>   	struct drm_writeback_connector *wb_conn = &output->wb_connector;
>   	struct drm_connector_state *conn_state = wb_conn->base.state;
>   	struct vkms_crtc_state *crtc_state = output->composer_state;
> +	struct drm_framebuffer *fb = connector_state->writeback_job->fb;
> +	struct vkms_writeback_job *active_wb;
> +	struct vkms_composer *wb_composer;
>   
>   	if (!conn_state)
>   		return;
>   
>   	vkms_set_composer(&vkmsdev->output, true);
>   
> +	active_wb = conn_state->writeback_job->priv;
> +	wb_composer = &active_wb->composer;
> +
>   	spin_lock_irq(&output->composer_lock);
> -	crtc_state->active_writeback = conn_state->writeback_job->priv;
> +	crtc_state->active_writeback = active_wb;
> +	memcpy(&wb_composer->fb, fb, sizeof(struct drm_framebuffer));
> +	wb_composer->offset = fb->offsets[0];
> +	wb_composer->pitch = fb->pitches[0];
> +	wb_composer->cpp = fb->format->cpp[0];

I don't know the exact cleanup requirements of these structures, but 
copying fb into composer looks like it breaks reference counting of the 
framebuffer's gem objects at least.

This atomic_commit helper would better acquire the correct references 
and hand them over to the compositor thread. Why not have a ref-counted 
composer or get a reference on the framebuffer instead?

Best regards
Thomas


>   	crtc_state->wb_pending = true;
>   	spin_unlock_irq(&output->composer_lock);
>   	drm_writeback_queue_job(wb_conn, connector_state);
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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