Re: [RFC PATCH] remoteproc: core: Add support for predefined notifyids

[Mathieu Poirier]

Hello Daniel,

On Fri, Oct 18, 2024 at 02:09:29PM +0300, Daniel Baluta wrote:
> Currently we generate notifyids in the linux kernel and override
> those found in rsc_table.
> 
> This doesn't play well with users expecting to use the exact ids
> from rsc_table.
> 
> So, use predefined notifyids found in rsc_table if any. Otherwise,
> let Linux generate the ids as before.
> 
> Keypoint is we also define an invalid notifid as 0xFFFFFFFFU. This
> should be placed as notifids if users want Linux to generate the ids.
> 
> Signed-off-by: Alexandru Lastur <alexandru.lastur@xxxxxxx>
> Signed-off-by: Daniel Baluta <daniel.baluta@xxxxxxx>
> ---
>  drivers/remoteproc/remoteproc_core.c | 14 ++++++++++++--
>  include/linux/remoteproc.h           |  1 +
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> index f276956f2c5c..9f00fe16da38 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -332,6 +332,7 @@ int rproc_alloc_vring(struct rproc_vdev *rvdev, int i)
>  	int ret, notifyid;
>  	struct rproc_mem_entry *mem;
>  	size_t size;
> +	int start, end;
>  
>  	/* actual size of vring (in bytes) */
>  	size = PAGE_ALIGN(vring_size(rvring->num, rvring->align));
> @@ -363,9 +364,18 @@ int rproc_alloc_vring(struct rproc_vdev *rvdev, int i)
>  	/*
>  	 * Assign an rproc-wide unique index for this vring
>  	 * TODO: assign a notifyid for rvdev updates as well
> -	 * TODO: support predefined notifyids (via resource table)
>  	 */
> -	ret = idr_alloc(&rproc->notifyids, rvring, 0, 0, GFP_KERNEL);
> +
> +	start = 0;
> +	end = 0;
> +
> +	/* use id if specified in rsc table */
> +	if (rsc->vring[i].notifyid != RSC_INVALID_NOTIFYID) {
> +		start = rsc->vring[i].notifyid;
> +		end = start + 1;
> +	}

This will likely introduce a backward compatibility issue where anyone that
has more than one vring and set their notifyids to anything else than 0xFFFFFFFF
in the resource table will see a boot failure.

A while back the openAMP group started discussions on using the configuration
space of a virtio device to enhance device discovery, with exactly this kind of
use case in mind.  I think it is the only way to move forward with this
feature, though it is a big job that requires a lot of community interactions.

Regards,
Mathieu

> +
> +	ret = idr_alloc(&rproc->notifyids, rvring, start, end, GFP_KERNEL);
>  	if (ret < 0) {
>  		dev_err(dev, "idr_alloc failed: %d\n", ret);
>  		return ret;
> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> index b4795698d8c2..98c3e181086e 100644
> --- a/include/linux/remoteproc.h
> +++ b/include/linux/remoteproc.h
> @@ -238,6 +238,7 @@ struct fw_rsc_trace {
>  	u8 name[32];
>  } __packed;
>  
> +#define RSC_INVALID_NOTIFYID 0xFFFFFFFFU
>  /**
>   * struct fw_rsc_vdev_vring - vring descriptor entry
>   * @da: device address
> -- 
> 2.43.0
>