Currently, the DPLL subsystem assumes that the only supported mode is
the one currently active on the device. When dpll_msg_add_mode_supported()
is called, it relies on ops->mode_get() and reports that single mode
to userspace. This prevents users from discovering other modes the device
might be capable of.

Add a new callback .supported_modes_get() to struct dpll_device_ops. This
allows drivers to populate a bitmap indicating all modes supported by
the hardware.

Update dpll_msg_add_mode_supported() to utilize this new callback:

* if ops->supported_modes_get is defined, use it to retrieve the full
  bitmap of supported modes.
* if not defined, fall back to the existing behavior: retrieve
  the current mode via ops->mode_get and set the corresponding bit
  in the bitmap.

Finally, iterate over the bitmap and add a DPLL_A_MODE_SUPPORTED netlink
attribute for every set bit, accurately reporting the device's capabilities
to userspace.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
 drivers/dpll/dpll_netlink.c | 27 +++++++++++++++++++--------
 include/linux/dpll.h        |  3 +++
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/drivers/dpll/dpll_netlink.c b/drivers/dpll/dpll_netlink.c
index 64944f601ee5a..d6a0e272d7038 100644
--- a/drivers/dpll/dpll_netlink.c
+++ b/drivers/dpll/dpll_netlink.c
@@ -128,18 +128,29 @@ dpll_msg_add_mode_supported(struct sk_buff *msg, struct dpll_device *dpll,
 			    struct netlink_ext_ack *extack)
 {
 	const struct dpll_device_ops *ops = dpll_device_ops(dpll);
+	DECLARE_BITMAP(modes, DPLL_MODE_MAX + 1) = { 0 };
 	enum dpll_mode mode;
 	int ret;
 
-	/* No mode change is supported now, so the only supported mode is the
-	 * one obtained by mode_get().
-	 */
+	if (ops->supported_modes_get) {
+		ret = ops->supported_modes_get(dpll, dpll_priv(dpll), modes,
+					       extack);
+		if (ret)
+			return ret;
+	} else {
+		/* If the supported modes are not reported by the driver, the
+		 * only supported mode is the one obtained by mode_get().
+		 */
+		ret = ops->mode_get(dpll, dpll_priv(dpll), &mode, extack);
+		if (ret)
+			return ret;
 
-	ret = ops->mode_get(dpll, dpll_priv(dpll), &mode, extack);
-	if (ret)
-		return ret;
-	if (nla_put_u32(msg, DPLL_A_MODE_SUPPORTED, mode))
-		return -EMSGSIZE;
+		__set_bit(mode, modes);
+	}
+
+	for_each_set_bit(mode, modes, DPLL_MODE_MAX + 1)
+		if (nla_put_u32(msg, DPLL_A_MODE_SUPPORTED, mode))
+			return -EMSGSIZE;
 
 	return 0;
 }
diff --git a/include/linux/dpll.h b/include/linux/dpll.h
index 562f520b23c27..912a2ca3e0ee7 100644
--- a/include/linux/dpll.h
+++ b/include/linux/dpll.h
@@ -20,6 +20,9 @@ struct dpll_pin_esync;
 struct dpll_device_ops {
 	int (*mode_get)(const struct dpll_device *dpll, void *dpll_priv,
 			enum dpll_mode *mode, struct netlink_ext_ack *extack);
+	int (*supported_modes_get)(const struct dpll_device *dpll,
+				   void *dpll_priv, unsigned long *modes,
+				   struct netlink_ext_ack *extack);
 	int (*lock_status_get)(const struct dpll_device *dpll, void *dpll_priv,
 			       enum dpll_lock_status *status,
 			       enum dpll_lock_status_error *status_error,
-- 
2.52.0

On 12/01/2026 10:14, Ivan Vecera wrote:
> Currently, the DPLL subsystem assumes that the only supported mode is
> the one currently active on the device. When dpll_msg_add_mode_supported()
> is called, it relies on ops->mode_get() and reports that single mode
> to userspace. This prevents users from discovering other modes the device
> might be capable of.
> 
> Add a new callback .supported_modes_get() to struct dpll_device_ops. This
> allows drivers to populate a bitmap indicating all modes supported by
> the hardware.
> 
> Update dpll_msg_add_mode_supported() to utilize this new callback:
> 
> * if ops->supported_modes_get is defined, use it to retrieve the full
>    bitmap of supported modes.
> * if not defined, fall back to the existing behavior: retrieve
>    the current mode via ops->mode_get and set the corresponding bit
>    in the bitmap.
> 
> Finally, iterate over the bitmap and add a DPLL_A_MODE_SUPPORTED netlink
> attribute for every set bit, accurately reporting the device's capabilities
> to userspace.
> 
> Signed-off-by: Ivan Vecera <ivecera@redhat.com>

LGTM,
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>