Re: [PATCH v2] remoteproc: core: Fetch the auto-boot firmware only once

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Wed, Sep 30, 2026 at 02:41:44PM +0800, Yonghao Zhang 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 <hyz3367@gmail.com>
> ---
> 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 | 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);

Please get rid of rproc_trigger_auto_boot() and call schedule_work() here.

Thanks,
Mathieu

>  
>  	/* 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
>