[PATCH 6/6] drm/gud: Use the shadow plane helper
Thomas Zimmermann
tzimmermann at suse.de
Wed Nov 23 10:38:48 UTC 2022
Hi
Am 22.11.22 um 21:58 schrieb Noralf Trønnes via B4 Submission Endpoint:
> From: Noralf Trønnes <noralf at tronnes.org>
>
> Use the shadow plane helper to take care of preparing the framebuffer for
> CPU access. The synchronous flushing is now done inline without the use of
> a worker. The async path now uses a shadow buffer to hold framebuffer
> changes and it doesn't read the framebuffer behind userspace's back
> anymore.
>
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> ---
> drivers/gpu/drm/gud/gud_drv.c | 1 +
> drivers/gpu/drm/gud/gud_internal.h | 1 +
> drivers/gpu/drm/gud/gud_pipe.c | 69 ++++++++++++++++++++++++--------------
> 3 files changed, 46 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/gpu/drm/gud/gud_drv.c b/drivers/gpu/drm/gud/gud_drv.c
> index d57dab104358..5aac7cda0505 100644
> --- a/drivers/gpu/drm/gud/gud_drv.c
> +++ b/drivers/gpu/drm/gud/gud_drv.c
> @@ -365,6 +365,7 @@ static void gud_debugfs_init(struct drm_minor *minor)
> static const struct drm_simple_display_pipe_funcs gud_pipe_funcs = {
> .check = gud_pipe_check,
> .update = gud_pipe_update,
> + DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS
> };
>
> static const struct drm_mode_config_funcs gud_mode_config_funcs = {
> diff --git a/drivers/gpu/drm/gud/gud_internal.h b/drivers/gpu/drm/gud/gud_internal.h
> index e351a1f1420d..0d148a6f27aa 100644
> --- a/drivers/gpu/drm/gud/gud_internal.h
> +++ b/drivers/gpu/drm/gud/gud_internal.h
> @@ -43,6 +43,7 @@ struct gud_device {
> struct drm_framebuffer *fb;
> struct drm_rect damage;
> bool prev_flush_failed;
> + void *shadow_buf;
> };
>
> static inline struct gud_device *to_gud_device(struct drm_device *drm)
> diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c
> index dfada6eedc58..7686325f7ee7 100644
> --- a/drivers/gpu/drm/gud/gud_pipe.c
> +++ b/drivers/gpu/drm/gud/gud_pipe.c
> @@ -358,10 +358,10 @@ static void gud_flush_damage(struct gud_device *gdrm, struct drm_framebuffer *fb
> void gud_flush_work(struct work_struct *work)
> {
> struct gud_device *gdrm = container_of(work, struct gud_device, work);
> - struct iosys_map gem_map = { }, fb_map = { };
> + struct iosys_map shadow_map;
> struct drm_framebuffer *fb;
> struct drm_rect damage;
> - int idx, ret;
> + int idx;
>
> if (!drm_dev_enter(&gdrm->drm, &idx))
> return;
> @@ -369,6 +369,7 @@ void gud_flush_work(struct work_struct *work)
> mutex_lock(&gdrm->damage_lock);
> fb = gdrm->fb;
> gdrm->fb = NULL;
> + iosys_map_set_vaddr(&shadow_map, gdrm->shadow_buf);
> damage = gdrm->damage;
> gud_clear_damage(gdrm);
> mutex_unlock(&gdrm->damage_lock);
> @@ -376,33 +377,33 @@ void gud_flush_work(struct work_struct *work)
> if (!fb)
> goto out;
>
> - ret = drm_gem_fb_vmap(fb, &gem_map, &fb_map);
> - if (ret)
> - goto fb_put;
> + gud_flush_damage(gdrm, fb, &shadow_map, true, &damage);
>
> - ret = drm_gem_fb_begin_cpu_access(fb, DMA_FROM_DEVICE);
> - if (ret)
> - goto vunmap;
> -
> - /* Imported buffers are assumed to be WriteCombined with uncached reads */
> - gud_flush_damage(gdrm, fb, &fb_map, !fb->obj[0]->import_attach, &damage);
> -
> - drm_gem_fb_end_cpu_access(fb, DMA_FROM_DEVICE);
> -vunmap:
> - drm_gem_fb_vunmap(fb, &gem_map);
> -fb_put:
> drm_framebuffer_put(fb);
> out:
> drm_dev_exit(idx);
> }
>
> -static void gud_fb_queue_damage(struct gud_device *gdrm, struct drm_framebuffer *fb,
> - struct drm_rect *damage)
> +static int gud_fb_queue_damage(struct gud_device *gdrm, struct drm_framebuffer *fb,
> + const struct iosys_map *map, struct drm_rect *damage)
> {
> struct drm_framebuffer *old_fb = NULL;
> + struct iosys_map shadow_map;
>
> mutex_lock(&gdrm->damage_lock);
>
> + if (!gdrm->shadow_buf) {
> + gdrm->shadow_buf = vzalloc(fb->pitches[0] * fb->height);
> + if (!gdrm->shadow_buf) {
> + mutex_unlock(&gdrm->damage_lock);
> + return -ENOMEM;
> + }
> + }
> +
> + iosys_map_set_vaddr(&shadow_map, gdrm->shadow_buf);
> + iosys_map_incr(&shadow_map, drm_fb_clip_offset(fb->pitches[0], fb->format, damage));
> + drm_fb_memcpy(&shadow_map, fb->pitches, map, fb, damage);
> +
It's all good (sans the begin_cpu_access issue) in terms of code, but
the memcpy here can have quite an impact on performace.
So why not just nuke the async code entirely? It's a userspace problem
and we don't have many(/any?) other drivers with such a workaround. Udl,
our other usb-based driver, works well enough without.
Best regards
Thomas
> if (fb != gdrm->fb) {
> old_fb = gdrm->fb;
> drm_framebuffer_get(fb);
> @@ -420,6 +421,26 @@ static void gud_fb_queue_damage(struct gud_device *gdrm, struct drm_framebuffer
>
> if (old_fb)
> drm_framebuffer_put(old_fb);
> +
> + return 0;
> +}
> +
> +static void gud_fb_handle_damage(struct gud_device *gdrm, struct drm_framebuffer *fb,
> + const struct iosys_map *map, struct drm_rect *damage)
> +{
> + int ret;
> +
> + if (gdrm->flags & GUD_DISPLAY_FLAG_FULL_UPDATE)
> + drm_rect_init(damage, 0, 0, fb->width, fb->height);
> +
> + if (gud_async_flush) {
> + ret = gud_fb_queue_damage(gdrm, fb, map, damage);
> + if (ret != -ENOMEM)
> + return;
> + }
> +
> + /* Imported buffers are assumed to be WriteCombined with uncached reads */
> + gud_flush_damage(gdrm, fb, map, !fb->obj[0]->import_attach, damage);
> }
>
> int gud_pipe_check(struct drm_simple_display_pipe *pipe,
> @@ -544,6 +565,7 @@ void gud_pipe_update(struct drm_simple_display_pipe *pipe,
> struct drm_device *drm = pipe->crtc.dev;
> struct gud_device *gdrm = to_gud_device(drm);
> struct drm_plane_state *state = pipe->plane.state;
> + struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(state);
> struct drm_framebuffer *fb = state->fb;
> struct drm_crtc *crtc = &pipe->crtc;
> struct drm_rect damage;
> @@ -557,6 +579,8 @@ void gud_pipe_update(struct drm_simple_display_pipe *pipe,
> gdrm->fb = NULL;
> }
> gud_clear_damage(gdrm);
> + vfree(gdrm->shadow_buf);
> + gdrm->shadow_buf = NULL;
> mutex_unlock(&gdrm->damage_lock);
> }
>
> @@ -572,13 +596,8 @@ void gud_pipe_update(struct drm_simple_display_pipe *pipe,
> if (crtc->state->active_changed)
> gud_usb_set_u8(gdrm, GUD_REQ_SET_DISPLAY_ENABLE, crtc->state->active);
>
> - if (drm_atomic_helper_damage_merged(old_state, state, &damage)) {
> - if (gdrm->flags & GUD_DISPLAY_FLAG_FULL_UPDATE)
> - drm_rect_init(&damage, 0, 0, fb->width, fb->height);
> - gud_fb_queue_damage(gdrm, fb, &damage);
> - if (!gud_async_flush)
> - flush_work(&gdrm->work);
> - }
> + if (drm_atomic_helper_damage_merged(old_state, state, &damage))
> + gud_fb_handle_damage(gdrm, fb, &shadow_plane_state->data[0], &damage);
>
> if (!crtc->state->enable)
> gud_usb_set_u8(gdrm, GUD_REQ_SET_CONTROLLER_ENABLE, 0);
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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