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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCPT_COUNT_TWELVE(0.00)[15]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[linux.intel.com,gmail.com,ffwll.ch,intel.com,linaro.org,kernel.org,ideasonboard.com,kwiboo.se,iki.fi,ti.com,lists.freedesktop.org,vger.kernel.org]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from,2a07:de40:b281:106:10:150:64:167:received]; TAGGED_RCPT(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim] X-Spam-Flag: NO X-Spam-Level: X-Rspamd-Queue-Id: 0F25E1F80C X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -3.01 Hi Am 23.09.25 um 11:37 schrieb Maxime Ripard: > On Mon, Sep 15, 2025 at 11:11:39AM +0200, Thomas Zimmermann wrote: >> Hi >> >> Am 15.09.25 um 10:42 schrieb Maxime Ripard: >>> Hi Tohmas, >>> >>> On Tue, Sep 02, 2025 at 03:44:54PM +0200, Thomas Zimmermann wrote: >>>>> +/** >>>>> + * drm_atomic_build_readout_state - Creates an initial state from the hardware >>>>> + * @dev: DRM device to build the state for >>>>> + * >>>>> + * This function allocates a &struct drm_atomic_state, calls the >>>>> + * atomic_readout_state callbacks, and fills the global state old states >>>>> + * by what the callbacks returned. >>>>> + * >>>>> + * Returns: >>>>> + * >>>>> + * A partially initialized &struct drm_atomic_state on success, an error >>>>> + * pointer otherwise. >>>>> + */ >>>>> +static struct drm_atomic_state * >>>>> +drm_atomic_build_readout_state(struct drm_device *dev) >>>>> +{ >>>>> + struct drm_connector_list_iter conn_iter; >>>>> + struct drm_atomic_state *state; >>>>> + struct drm_mode_config *config = >>>>> + &dev->mode_config; >>>>> + struct drm_connector *connector; >>>>> + struct drm_printer p = >>>>> + drm_info_printer(dev->dev); >>>>> + struct drm_encoder *encoder; >>>>> + struct drm_plane *plane; >>>>> + struct drm_crtc *crtc; >>>>> + int ret; >>>>> + >>>>> + drm_dbg_kms(dev, "Starting to build atomic state from hardware state.\n"); >>>>> + >>>>> + state = drm_atomic_state_alloc(dev); >>>>> + if (WARN_ON(!state)) >>>>> + return ERR_PTR(-ENOMEM); >>>>> + >>>>> + state->connectors = kcalloc(config->num_connector, sizeof(*state->connectors), GFP_KERNEL); >>>>> + if (WARN_ON(!state->connectors)) { >>>>> + ret = -ENOMEM; >>>>> + goto err_state_put; >>>>> + } >>>>> + >>>>> + state->private_objs = kcalloc(count_private_obj(dev), sizeof(*state->private_objs), GFP_KERNEL); >>>>> + if (WARN_ON(!state->private_objs)) { >>>>> + ret = -ENOMEM; >>>>> + goto err_state_put; >>>>> + } >>>>> + >>>>> + drm_for_each_crtc(crtc, dev) { >>>>> + const struct drm_crtc_funcs *crtc_funcs = >>>>> + crtc->funcs; >>>>> + struct drm_crtc_state *crtc_state; >>>>> + >>>>> + drm_dbg_kms(dev, "Initializing CRTC %s state.\n", crtc->name); >>>>> + >>>>> + if (crtc_funcs->atomic_readout_state) { >>>>> + crtc_state = crtc_funcs->atomic_readout_state(crtc); >>>>> + } else if (crtc_funcs->reset) { >>>>> + crtc_funcs->reset(crtc); >>>>> + >>>>> + /* >>>>> + * We don't want to set crtc->state field yet. Let's save and clear it up. >>>>> + */ >>>>> + crtc_state = crtc->state; >>>>> + crtc->state = NULL; >>>> Chancing the crtc->state pointer behind the back of the reset callback seems >>>> fragile. We never how if some other piece of the driver refers to it >>>> (although illegally). >>> I agree that it's clunky. I'm not sure who would use it at this point >>> though: we're in the middle of the drm_mode_config_reset(), so the >>> drivers' involvement is pretty minimal. >>> >>> I did wonder if changing reset to return the object instead of setting >>> $OBJECT->state would be a better interface? >> Probably not. The reset helper is supposed to initialize the object's >> software and hardware state. But in most drivers, we're currently mostly >> setting the minimal software state here and simply assume that hardware is >> off. Returning the state would water down semantics even further. >> >> Having said that, I could imaging building an atomic_clean_state callback >> that replaces the reset callback. It would work alongside the new >> atomic_readout_state callback.  Current reset could be build upon that >> callback. The atomic_clean_state would intentionally only take care of the >> software state and leave hardware state undefined. This reflects the current >> realities of most DRM drivers.   From that clean state, DRM could do an >> atomic commit that also initializes the hardware. > That sounds like a good idea, but I wonder how we would deal with reset > then? Should we remove it entirely? Still call it? What do you think? I think in that design, a reset would be atomic_clean_state + atomic_commit. The clean_state step would likely always happen, were we currently do the reset. In the long term, the commit step could be moved into drm_dev_register() or even the DRM client setup. The later place should make it easy for in-kernel DRM clients to adopt the current display config.  If there's no client enabled, a plain atomic_commit would set the HW to whatever is in the state. The state could, of course, also come from atomic_readout_state in which case in which the display would just keep running as-is on the atomic_commit. Best regards Thomas > >>>> For now, wouldn't it be better to require a read-out helper for all elements >>>> of the driver's mode-setting pipeline?  The trivial implementation would >>>> copy the existing reset function and keep crtc->state to NULL. >>> I also considered that, but I'm not sure we can expect bridges to have >>> readout hooks filled for every configuration in the wild. >>> >>> But maybe we can look during drm_mode_config_reset() at whether all the >>> objects have their hook filled, and if not fall back on reset for >>> everything. >> That's what I meant, I think. >> >>> It would make the implementation easier, but missing bridges >>> implementations would trigger a mode change when it might actually work >>> just fine since bridge state is pretty minimal. >> If there's an element in the pipeline that's missing the readout helper, it >> might be safer to fallback to that modeset instead of ending up with >> inconsistent state. > Yeah, that sounds fair. > > Maxime -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)