Re: [PATCH v2 1/2] remoteproc: core: support fixed device index from DT aliases

[Peng Fan <peng.fan@oss.nxp.com>]

On Wed, Jan 28, 2026 at 11:31:17AM +0100, Arnaud Pouliquen wrote:
>On systems with multiple remote processors, the remoteproc device
>enumeration is not stable as it depends on the probe ordering.
>As a result, the /sys/class/remoteproc/remoteproc<x> entries do not
>always refer to the same remote processor instance, which complicates
>userspace applications.
>
>Inspired by the SPI implementation, this commit allows board-specific
>numbering to be defined in device tree while still supporting dynamically
>registered remote processors.
>
>For instance, on STM32MP25 Soc this can be used by defining:
>
>    aliases {
>        rproc0 = &m33_rproc;
>        rproc1 = &m0_rproc;
>    };
>
>When a "rproc<x>" DT alias is present, use it to assign a fixed
>"/sys/class/remoteproc/remoteproc<x>" entry.
>If no remoteproc alias is defined, keep the legacy index allocation.
>If only some remoteproc instances have an alias, allocate dynamic
>index starting after the highest alias index declared.
>
>Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

Tested this patch on i.MX943-EVK(patches for this platform still in my local)
with dual CM7 and one CM33S:
/sys/devices/platform/imx943-cm70/remoteproc/remoteproc1/firmware
/sys/devices/platform/imx943-cm33s/remoteproc/remoteproc0/firmware
/sys/devices/platform/imx943-cm71/remoteproc/remoteproc2/firmware

Tested-by: Peng Fan <peng.fan@nxp.com>

One nit below:

>---
>V2:
>- Introduces rproc_get_index based on Mathieu Poirier's suggestion.
>  An update compared to Mathieu's version is that the call to
>  ida_alloc_range is retained if an alias is found for the remote device,
>  to balance with ida_free().
>- Rename DT alias stem from "remoteproc" to "rproc" to be consistent with
>  keytone driver.
>---
> drivers/remoteproc/remoteproc_core.c | 40 ++++++++++++++++++++++++++--
> include/linux/remoteproc.h           |  3 +++
> 2 files changed, 41 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
>index aada2780b343..38d6eb1c9483 100644
>--- a/drivers/remoteproc/remoteproc_core.c
>+++ b/drivers/remoteproc/remoteproc_core.c
>@@ -2433,6 +2433,43 @@ static int rproc_alloc_ops(struct rproc *rproc, const struct rproc_ops *ops)
> 	return 0;
> }
> 
>+/**
>+ * rproc_get_index - assign a unique device index for a remote processor
>+ * @dev: device associated with the remote processor
>+ *
>+ * Look for a static index coming from the "rproc" DT alias
>+ * (e.g. "rproc0"). If none is found, start allocating
>+ * dynamic IDs after the highest alias in use.
>+ *
>+ * Return: a non-negative index on success, or a negative error code on failure.
>+ */
>+static int rproc_get_index(struct device *dev)
>+{
>+	int index;
>+
>+	/* No DT to deal with */
>+	if (!dev->of_node)
>+		goto legacy;
>+
>+	/* See if an alias has been assigned to this remoteproc */
>+	index = of_alias_get_id(dev->of_node, RPROC_ALIAS);
>+	if (index >= 0)
>+		return  ida_alloc_range(&rproc_dev_index, index, index,
>+					GFP_KERNEL);

Nit: "return ida_alloc_range"

Regards,
Peng