[PATCH v2 1/5] firmware: arm_scmi: Account for SHMEM memory overhead

[Florian Fainelli]

On 10/21/24 10:07, Cristian Marussi wrote:
> Transports using shared memory have to consider the overhead due to the
> layout area when determining the area effectively available for messages.
> 
> Till now, such definitions were ambiguos across the SCMI stack and the
> overhead layout area was not considered at all.
> 
> Add proper checks in the shmem layer to validate the provided max_msg_size
> against the effectively available memory area, less the layout.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi at arm.com>
> ---
> Note that as a consequence of this fix the default max_msg_size is reduced
> to 104 bytes for shmem-based transports, in order to fit into the most
> common implementations where the whole shmem area is sized at 128,
> including the 24 bytes of standard layout area.
> 
> This should have NO bad side effects, since the current maximum payload
> size of any messages across any protocol (including all the known vendor
> ones) is 76 bytes.

This looks good to me, just a small nit/suggestion:

[snip]

>   	size = resource_size(res);
> +	if (cinfo->max_msg_size + SCMI_SHMEM_LAYOUT_OVERHEAD > size) {
> +		dev_err(dev, "misconfigured SCMI shared memory\n");
> +		return IOMEM_ERR_PTR(-ENOSPC);
> +	}
> +
>   	addr = devm_ioremap(dev, res->start, size);
>   	if (!addr) {
>   		dev_err(dev, "failed to ioremap SCMI %s shared memory\n", desc);
> diff --git a/drivers/firmware/arm_scmi/transports/mailbox.c b/drivers/firmware/arm_scmi/transports/mailbox.c
> index e7efa3376aae..4e0396250ad0 100644
> --- a/drivers/firmware/arm_scmi/transports/mailbox.c
> +++ b/drivers/firmware/arm_scmi/transports/mailbox.c
> @@ -16,6 +16,8 @@
>   
>   #include "../common.h"
>   
> +#define SCMI_MAILBOX_MAX_MSG_SIZE	104

This IMHO, could be named SCMI_SHMEM_MAX_PAYLOAD_SIZE and used across 
all 3 transports that are loosely SHMEM-based?
-- 
Florian