On Thu, 1 Oct 2026 at 02:11, Yonghao Zhang <[email protected]> wrote:
>
> Auto-boot for an always-on remote processor registers an asynchronous
> request_firmware_nowait() whose callback, rproc_auto_boot_callback(),
> calls rproc_boot() first and only releases the fetched image at the
> very end of the callback. rproc_boot() does not take this image as an
> argument: it 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 processor 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 <[email protected]>
> ---
> Changes in v3:
> - Drop rproc_trigger_auto_boot() wrapper and schedule boot_work
> directly in rproc_add() (Mathieu).
>
> Changes in v2:
> - Fix the order described in the changelog: the callback calls
> rproc_boot() first and releases the asynchronously fetched image at
> the end of the callback (Mathieu).
> - Fix typo "proccessor".
>
> drivers/remoteproc/remoteproc_core.c | 66 +++++++---------------------
> include/linux/remoteproc.h | 4 +-
> 2 files changed, 19 insertions(+), 51 deletions(-)
>
I will apply this patch when 7.4-rc1 comes out.
> diff --git a/drivers/remoteproc/remoteproc_core.c
> b/drivers/remoteproc/remoteproc_core.c
> index 263e12f022ea..b88bf179507d 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -1662,51 +1662,23 @@ 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: 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)
> -{
> - struct rproc *rproc = context;
> -
> - rproc_boot(rproc);
> -
> - release_firmware(fw);
> -}
> -
> -static void rproc_attach_work(struct work_struct *work)
> +static void rproc_boot_work(struct work_struct *work)
> {
> - struct rproc *rproc = container_of(work, struct rproc, attach_work);
> + struct rproc *rproc = container_of(work, struct rproc, boot_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;
> -}
> -
> static int rproc_stop(struct rproc *rproc, bool crashed)
> {
> struct device *dev = &rproc->dev;
> @@ -2348,11 +2320,8 @@ 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)
> + schedule_work(&rproc->boot_work);
>
> /* expose to rproc_get_by_phandle users */
> mutex_lock(&rproc_list_mutex);
> @@ -2361,10 +2330,6 @@ 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 +2517,7 @@ 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 +2595,9 @@ 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
>
