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

[Arnaud POULIQUEN]

hello

On 10/23/24 17:32, Mathieu Poirier wrote:
> 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.
> 
FYI a PR exists in OpenAMP to use this configuration space to customize the
size of the buffers [2].

This probably means we need something scalable for the configuration space.

I guess your objective is to match the vring ID with the mailbox channel ID, right?
We have a similar issue with the STM32MP1/2. It is hard-coded in the stm32_rproc
driver[1], which is far from perfect because it is not simple to add a new vdev
instance.

I would have two other alternatives to highlight

- An alternative could be to have a vendor resource in the resource table and
use rproc_handle_rsc operations. This resource would define the match between the
vrings IDs and the mailbox IDs.
However, if several vendors are facing the same issue, perhaps better to find a
generic solution.

- another alternative already discussed several times in openAMP group would be
to define a new version of the resource table.

[1]https://elixir.bootlin.com/linux/v6.11/source/drivers/remoteproc/stm32_rproc.c#L328
[2] https://github.com/OpenAMP/open-amp/pull/155

Regards
Arnaud

> 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
>>
>