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([2a01:e0a:c:37e0:8998:e0cf:68cc:1b62]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cb7fa41d2sm9780925f8f.22.2025.11.21.01.15.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Nov 2025 01:15:14 -0800 (PST) Message-ID: <3fce43d9-260a-4539-9b25-3dff42c4fdd7@redhat.com> Date: Fri, 21 Nov 2025 10:15:13 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] drm/client: Support emergency restore via sysrq for all clients To: Thomas Zimmermann , javierm@redhat.com, francesco@valla.it, rrameshbabu@nvidia.com, simona@ffwll.ch, airlied@gmail.com, mripard@kernel.org, maarten.lankhorst@linux.intel.com, gregkh@linuxfoundation.org, jirislaby@kernel.org Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org References: <20251110154616.539328-1-tzimmermann@suse.de> <20251110154616.539328-3-tzimmermann@suse.de> Content-Language: en-US, fr From: Jocelyn Falempe In-Reply-To: <20251110154616.539328-3-tzimmermann@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/11/2025 16:44, Thomas Zimmermann wrote: > Move the sysrq functionality from DRM fbdev helpers to the DRM device > and in-kernel clients, so that it becomes available on all clients. > > DRM fbdev helpers support emergency restoration of the console output > via a special key combination. Press SysRq+v to replace the current > compositor with the kernel's output on the framebuffer console. This > allows users to see the log messages during system emergencies. > > By moving the functionality from fbdev helpers to the DRM device, any > in-kernel client can serve as emergency output. This can be used to > bring up drm_log, for example. > > Each DRM device registers itself to the list of possible sysrq handlers. > On receiving SysRq+v, the DRM core goes over all registered devices and > restores an in-kernel DRM client for each of them. > > See Documentation/admin-guide/sysrq.rst on how to invoke SysRq. Switch > VTs to bring back the user-space compositor. > Thanks, it looks good to me. Reviewed-by: Jocelyn Falempe > v2: > - declare placeholders as 'static inline' (kernel test robot) > - fix grammar in commit description > > Signed-off-by: Thomas Zimmermann > --- > drivers/gpu/drm/Makefile | 3 +- > drivers/gpu/drm/drm_client.c | 1 + > drivers/gpu/drm/drm_client_sysrq.c | 65 ++++++++++++++++++++++++++++++ > drivers/gpu/drm/drm_drv.c | 3 ++ > drivers/gpu/drm/drm_fb_helper.c | 45 +-------------------- > drivers/gpu/drm/drm_internal.h | 11 +++++ > include/drm/drm_device.h | 8 ++++ > 7 files changed, 91 insertions(+), 45 deletions(-) > create mode 100644 drivers/gpu/drm/drm_client_sysrq.c > > diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile > index 7789f42027ff..33ff76ae52b2 100644 > --- a/drivers/gpu/drm/Makefile > +++ b/drivers/gpu/drm/Makefile > @@ -76,7 +76,8 @@ drm-y := \ > drm-$(CONFIG_DRM_CLIENT) += \ > drm_client.o \ > drm_client_event.o \ > - drm_client_modeset.o > + drm_client_modeset.o \ > + drm_client_sysrq.o > drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o > drm-$(CONFIG_COMPAT) += drm_ioc32.o > drm-$(CONFIG_DRM_PANEL) += drm_panel.o > diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c > index 504ec5bdfa2c..a82d741e6630 100644 > --- a/drivers/gpu/drm/drm_client.c > +++ b/drivers/gpu/drm/drm_client.c > @@ -11,6 +11,7 @@ > #include > > #include > +#include > #include > #include > #include > diff --git a/drivers/gpu/drm/drm_client_sysrq.c b/drivers/gpu/drm/drm_client_sysrq.c > new file mode 100644 > index 000000000000..eea660096f1b > --- /dev/null > +++ b/drivers/gpu/drm/drm_client_sysrq.c > @@ -0,0 +1,65 @@ > +// SPDX-License-Identifier: GPL-2.0 or MIT > + > +#include > + > +#include > +#include > +#include > + > +#include "drm_internal.h" > + > +#ifdef CONFIG_MAGIC_SYSRQ > +static LIST_HEAD(drm_client_sysrq_dev_list); > +static DEFINE_MUTEX(drm_client_sysrq_dev_lock); > + > +/* emergency restore, don't bother with error reporting */ > +static void drm_client_sysrq_restore_work_fn(struct work_struct *ignored) > +{ > + struct drm_device *dev; > + > + guard(mutex)(&drm_client_sysrq_dev_lock); > + > + list_for_each_entry(dev, &drm_client_sysrq_dev_list, client_sysrq_list) { > + if (dev->switch_power_state == DRM_SWITCH_POWER_OFF) > + continue; > + > + drm_client_dev_restore(dev, true); > + } > +} > + > +static DECLARE_WORK(drm_client_sysrq_restore_work, drm_client_sysrq_restore_work_fn); > + > +static void drm_client_sysrq_restore_handler(u8 ignored) > +{ > + schedule_work(&drm_client_sysrq_restore_work); > +} > + > +static const struct sysrq_key_op drm_client_sysrq_restore_op = { > + .handler = drm_client_sysrq_restore_handler, > + .help_msg = "force-fb(v)", > + .action_msg = "Restore framebuffer console", > +}; > + > +void drm_client_sysrq_register(struct drm_device *dev) > +{ > + guard(mutex)(&drm_client_sysrq_dev_lock); > + > + if (list_empty(&drm_client_sysrq_dev_list)) > + register_sysrq_key('v', &drm_client_sysrq_restore_op); > + > + list_add(&dev->client_sysrq_list, &drm_client_sysrq_dev_list); > +} > + > +void drm_client_sysrq_unregister(struct drm_device *dev) > +{ > + guard(mutex)(&drm_client_sysrq_dev_lock); > + > + /* remove device from global restore list */ > + if (!drm_WARN_ON(dev, list_empty(&dev->client_sysrq_list))) > + list_del(&dev->client_sysrq_list); > + > + /* no devices left; unregister key */ > + if (list_empty(&drm_client_sysrq_dev_list)) > + unregister_sysrq_key('v', &drm_client_sysrq_restore_op); > +} > +#endif > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c > index 8e3cb08241c8..2915118436ce 100644 > --- a/drivers/gpu/drm/drm_drv.c > +++ b/drivers/gpu/drm/drm_drv.c > @@ -733,6 +733,7 @@ static int drm_dev_init(struct drm_device *dev, > INIT_LIST_HEAD(&dev->filelist); > INIT_LIST_HEAD(&dev->filelist_internal); > INIT_LIST_HEAD(&dev->clientlist); > + INIT_LIST_HEAD(&dev->client_sysrq_list); > INIT_LIST_HEAD(&dev->vblank_event_list); > > spin_lock_init(&dev->event_lock); > @@ -1100,6 +1101,7 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags) > goto err_unload; > } > drm_panic_register(dev); > + drm_client_sysrq_register(dev); > > DRM_INFO("Initialized %s %d.%d.%d for %s on minor %d\n", > driver->name, driver->major, driver->minor, > @@ -1144,6 +1146,7 @@ void drm_dev_unregister(struct drm_device *dev) > { > dev->registered = false; > > + drm_client_sysrq_unregister(dev); > drm_panic_unregister(dev); > > drm_client_dev_unregister(dev); > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > index 1392738ce2fe..9a734017756b 100644 > --- a/drivers/gpu/drm/drm_fb_helper.c > +++ b/drivers/gpu/drm/drm_fb_helper.c > @@ -32,7 +32,6 @@ > #include > #include > #include > -#include > #include > > #include > @@ -270,42 +269,6 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper, b > } > EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked); > > -#ifdef CONFIG_MAGIC_SYSRQ > -/* emergency restore, don't bother with error reporting */ > -static void drm_fb_helper_restore_work_fn(struct work_struct *ignored) > -{ > - struct drm_fb_helper *helper; > - > - mutex_lock(&kernel_fb_helper_lock); > - list_for_each_entry(helper, &kernel_fb_helper_list, kernel_fb_list) { > - struct drm_device *dev = helper->dev; > - > - if (dev->switch_power_state == DRM_SWITCH_POWER_OFF) > - continue; > - > - mutex_lock(&helper->lock); > - drm_client_modeset_commit_locked(&helper->client); > - mutex_unlock(&helper->lock); > - } > - mutex_unlock(&kernel_fb_helper_lock); > -} > - > -static DECLARE_WORK(drm_fb_helper_restore_work, drm_fb_helper_restore_work_fn); > - > -static void drm_fb_helper_sysrq(u8 dummy1) > -{ > - schedule_work(&drm_fb_helper_restore_work); > -} > - > -static const struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { > - .handler = drm_fb_helper_sysrq, > - .help_msg = "force-fb(v)", > - .action_msg = "Restore framebuffer console", > -}; > -#else > -static const struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { }; > -#endif > - > static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode) > { > struct drm_fb_helper *fb_helper = info->par; > @@ -602,11 +565,8 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper) > drm_fb_helper_release_info(fb_helper); > > mutex_lock(&kernel_fb_helper_lock); > - if (!list_empty(&fb_helper->kernel_fb_list)) { > + if (!list_empty(&fb_helper->kernel_fb_list)) > list_del(&fb_helper->kernel_fb_list); > - if (list_empty(&kernel_fb_helper_list)) > - unregister_sysrq_key('v', &sysrq_drm_fb_helper_restore_op); > - } > mutex_unlock(&kernel_fb_helper_lock); > > if (!fb_helper->client.funcs) > @@ -1840,9 +1800,6 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper) > info->node, info->fix.id); > > mutex_lock(&kernel_fb_helper_lock); > - if (list_empty(&kernel_fb_helper_list)) > - register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op); > - > list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list); > mutex_unlock(&kernel_fb_helper_lock); > > diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h > index 5a3bed48ab1f..f893b1e3a596 100644 > --- a/drivers/gpu/drm/drm_internal.h > +++ b/drivers/gpu/drm/drm_internal.h > @@ -56,6 +56,17 @@ static inline void drm_client_debugfs_init(struct drm_device *dev) > { } > #endif > > +/* drm_client_sysrq.c */ > +#if defined(CONFIG_DRM_CLIENT) && defined(CONFIG_MAGIC_SYSRQ) > +void drm_client_sysrq_register(struct drm_device *dev); > +void drm_client_sysrq_unregister(struct drm_device *dev); > +#else > +static inline void drm_client_sysrq_register(struct drm_device *dev) > +{ } > +static inline void drm_client_sysrq_unregister(struct drm_device *dev) > +{ } > +#endif > + > /* drm_file.c */ > extern struct mutex drm_global_mutex; > bool drm_dev_needs_global_mutex(struct drm_device *dev); > diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h > index 778b2cca6c49..5af49c5c3778 100644 > --- a/include/drm/drm_device.h > +++ b/include/drm/drm_device.h > @@ -238,6 +238,14 @@ struct drm_device { > */ > struct list_head clientlist; > > + /** > + * @client_sysrq_list: > + * > + * Entry into list of devices registered for sysrq. Allows in-kernel > + * clients on this device to handle sysrq keys. > + */ > + struct list_head client_sysrq_list; > + > /** > * @vblank_disable_immediate: > *