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Mon, 28 Sep 2026 10:34:16 -0700 (PDT) Date: Mon, 28 Sep 2026 11:34:14 -0600 From: Mathieu Poirier To: Yonghao Zhang Cc: andersson@kernel.org, linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] remoteproc: core: Fetch the auto-boot firmware only once Message-ID: References: <20260923025855.2523147-1-hyz3367@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923025855.2523147-1-hyz3367@gmail.com> Good day, On Wed, Sep 23, 2026 at 10:58:55AM +0800, Yonghao Zhang wrote: > Auto-boot for an always-on remote processor registers an asynchronous > request_firmware_nowait() whose callback discards the fetched image The callback function is rproc_auto_boot_callback() but I don't see where the image fetched by request_firmware_nowait() is discarded. Otherwise I agree with this patch. Thanks, Mathieu > and calls rproc_boot(). rproc_boot() then fetches the very same image > again with a synchronous request_firmware(), so every auto-boot reads > the firmware image twice and allocates the buffer twice; on kernels > with the sysfs fallback enabled, the uevent round-trip is repeated > as well. > > The asynchronous request exists only so that rproc_add() does not > block on the filesystem read; the image it fetches is never used. > The core already defers rproc_boot() to a worker for detached > processors (attach_work). Reuse that worker for offline processors > too and drop the asynchronous firmware request: rproc_boot() fetches > the image exactly once and dispatches between a firmware boot and > an attach based on the proccessor state. The work is renamed to > boot_work to match its widened role. > > commit 400e64df6b23 ("remoteproc: add framework for controlling remote > processors") noted back in 2011 that "we must wait until it completes > before we try to unregister the device". rproc_del() now does exactly > that: it waits for the boot work with cancel_work_sync(), which also > closes the theoretical window in which a pending attach work could > outlive the rproc instance. > > The changed fallback behaviour only matters for legacy > configurations. udev dropped its userspace firmware loader back in > 2014, as recorded in > Documentation/driver-api/firmware/fallback-mechanisms.rst, and the > kernel has documented since commit 02c399306826 ("firmware_loader: > enhance Kconfig documentation over FW_LOADER") that "Linux no longer > relies on or uses a fallback mechanism in userspace". Auto-boot now > uses the same synchronous fallback semantics as every other explicit > boot source (sysfs, cdev). > > Signed-off-by: Yonghao Zhang > --- > drivers/remoteproc/remoteproc_core.c | 65 ++++++++-------------------- > include/linux/remoteproc.h | 4 +- > 2 files changed, 21 insertions(+), 48 deletions(-) > > diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c > index 263e12f022ea..f329dc478170 100644 > --- a/drivers/remoteproc/remoteproc_core.c > +++ b/drivers/remoteproc/remoteproc_core.c > @@ -1662,49 +1662,26 @@ static int rproc_attach(struct rproc *rproc) > } > > /* > - * take a firmware and boot it up. > - * > - * Note: this function is called asynchronously upon registration of the > - * remote processor (so we must wait until it completes before we try > - * to unregister the device. one other option is just to use kref here, > - * that might be cleaner). > + * Boot or attach the remote processor in the background, on behalf of > + * rproc_trigger_auto_boot(): rproc_add() runs in probe context and must > + * not block while the firmware image is read from storage. rproc_boot() > + * dispatches on the processor state, so this covers both a firmware boot > + * and an attach to a processor started by another entity. > + * > + * Note: rproc_del() waits for this work to complete with > + * cancel_work_sync(), so the rproc instance remains valid for the > + * entire lifetime of this function. > */ > -static void rproc_auto_boot_callback(const struct firmware *fw, void *context) > +static void rproc_boot_work(struct work_struct *work) > { > - struct rproc *rproc = context; > + struct rproc *rproc = container_of(work, struct rproc, boot_work); > > rproc_boot(rproc); > - > - release_firmware(fw); > } > > -static void rproc_attach_work(struct work_struct *work) > +static void rproc_trigger_auto_boot(struct rproc *rproc) > { > - struct rproc *rproc = container_of(work, struct rproc, attach_work); > - > - rproc_boot(rproc); > -} > - > -static int rproc_trigger_auto_boot(struct rproc *rproc) > -{ > - int ret; > - > - if (rproc->state == RPROC_DETACHED) { > - schedule_work(&rproc->attach_work); > - return 0; > - } > - > - /* > - * We're initiating an asynchronous firmware loading, so we can > - * be built-in kernel code, without hanging the boot process. > - */ > - ret = request_firmware_nowait(THIS_MODULE, FW_ACTION_UEVENT, > - rproc->firmware, &rproc->dev, GFP_KERNEL, > - rproc, rproc_auto_boot_callback); > - if (ret < 0) > - dev_err(&rproc->dev, "request_firmware_nowait err: %d\n", ret); > - > - return ret; > + schedule_work(&rproc->boot_work); > } > > static int rproc_stop(struct rproc *rproc, bool crashed) > @@ -2348,11 +2325,8 @@ int rproc_add(struct rproc *rproc) > rproc_create_debug_dir(rproc); > > /* if rproc is marked always-on, request it to boot */ > - if (rproc->auto_boot) { > - ret = rproc_trigger_auto_boot(rproc); > - if (ret < 0) > - goto rproc_remove_dev; > - } > + if (rproc->auto_boot) > + rproc_trigger_auto_boot(rproc); > > /* expose to rproc_get_by_phandle users */ > mutex_lock(&rproc_list_mutex); > @@ -2361,10 +2335,6 @@ int rproc_add(struct rproc *rproc) > > return 0; > > -rproc_remove_dev: > - cancel_work_sync(&rproc->crash_handler); > - rproc_delete_debug_dir(rproc); > - device_del(dev); > rproc_remove_cdev: > rproc_char_device_remove(rproc); > return ret; > @@ -2552,7 +2522,7 @@ struct rproc *rproc_alloc(struct device *dev, const char *name, > INIT_LIST_HEAD(&rproc->subdevs); > INIT_LIST_HEAD(&rproc->dump_segments); > > - INIT_WORK(&rproc->attach_work, rproc_attach_work); > + INIT_WORK(&rproc->boot_work, rproc_boot_work); > INIT_WORK(&rproc->crash_handler, rproc_crash_handler_work); > spin_lock_init(&rproc->crash_handler_lock); > > @@ -2630,6 +2600,9 @@ int rproc_del(struct rproc *rproc) > if (cancel_work_sync(&rproc->crash_handler)) > pm_relax(rproc->dev.parent); > > + /* auto-boot may still be fetching firmware: wait for it here */ > + cancel_work_sync(&rproc->boot_work); > + > __rproc_shutdown(rproc, true); > > rproc_delete_debug_dir(rproc); > diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h > index a44368737b39..d77e24539133 100644 > --- a/include/linux/remoteproc.h > +++ b/include/linux/remoteproc.h > @@ -231,7 +231,7 @@ enum rproc_features { > * @subdevs: list of subdevices, to following the running state > * @notifyids: idr for dynamically assigning rproc-wide unique notify ids > * @index: index of this rproc device > - * @attach_work: workqueue for attaching rproc > + * @boot_work: workqueue for booting rproc > * @crash_handler: workqueue for handling a crash > * @crash_handler_lock: serializes crash handler queueing and deletion > * @deleting: remoteproc deletion has begun > @@ -277,7 +277,7 @@ struct rproc { > struct list_head subdevs; > struct idr notifyids; > int index; > - struct work_struct attach_work; > + struct work_struct boot_work; > struct work_struct crash_handler; > spinlock_t crash_handler_lock; > bool deleting; > -- > 2.34.1 >