[PATCH 1/2] dm: core: add support for fallback drivers

[Heinrich Schuchardt]

Am 10. April 2024 19:06:57 MESZ schrieb Caleb Connolly <caleb.connolly at linaro.org>:
>Introduce support for a uclass to provide a fallback/stub driver which
>can be used when no device is found for a given node. This might be
>useful for handling non-essential clock controllers like the RPMh on
>Qualcomm platforms, or during early bringup to get UART output before a
>real clock driver has been created.
>
>Signed-off-by: Caleb Connolly <caleb.connolly at linaro.org>
>---
> drivers/core/Kconfig  | 10 ++++++++++
> drivers/core/uclass.c | 24 +++++++++++++++++++++++-
> include/dm/uclass.h   |  3 +++
> 3 files changed, 36 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/core/Kconfig b/drivers/core/Kconfig
>index 1081d61fcf01..09075b9b7a15 100644
>--- a/drivers/core/Kconfig
>+++ b/drivers/core/Kconfig
>@@ -466,5 +466,15 @@ config BOUNCE_BUFFER
> 
> 	  A second possible use of bounce buffers is their ability to
> 	  provide aligned buffers for DMA operations.
> 
>+menuconfig FALLBACK_DRIVERS

Wouldn't it be preferable to mark individual drivers as fallback drivers in their declaration?

This would allow alternative fallback drivers and would not require any definitions at uclass level.

Just by building a fallback driver you would enable the fallback behavior for its uclass.

Best regards

Heinrich

>+	bool "Enable per-uclass fallback drivers"
>+	depends on DM
>+	help
>+	  If a driver requests a resource (like a clock) from a node which
>+	  isn't bound to a driver, the driver model will look for a fallback
>+	  driver to "stub" the resource. These stubs usually do nothing and
>+	  are therefore only suitable in instances where the resource is not
>+	  required.
>+
> endmenu
>diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
>index e46d5717aa62..91d3a48d77b8 100644
>--- a/drivers/core/uclass.c
>+++ b/drivers/core/uclass.c
>@@ -378,8 +378,26 @@ int uclass_find_device_by_of_offset(enum uclass_id id, int node,
> 
> 	return -ENODEV;
> }
> 
>+static int uclass_bind_fallback(struct uclass *uc, ofnode node, struct udevice **devp)
>+{
>+	struct driver *drv;
>+
>+	log(LOGC_DM, LOGL_ERR, "   - binding fallback '%s' driver '%s'\n",
>+	    uc->uc_drv->name, uc->uc_drv->fallback_drv_name);
>+
>+	drv = lists_driver_lookup_name(uc->uc_drv->fallback_drv_name);
>+	if (!drv) {
>+		log(LOGC_DM, LOGL_DEBUG, "   - Can't find stub driver '%s' for uclass '%s'\n",
>+		    uc->uc_drv->fallback_drv_name, uc->uc_drv->name);
>+		return -ENOENT;
>+	}
>+
>+	return device_bind_with_driver_data(gd->dm_root, drv,
>+					  ofnode_get_name(node), 0, node, devp);
>+}
>+
> int uclass_find_device_by_ofnode(enum uclass_id id, ofnode node,
> 				 struct udevice **devp)
> {
> 	struct uclass *uc;
>@@ -401,9 +419,13 @@ int uclass_find_device_by_ofnode(enum uclass_id id, ofnode node,
> 			*devp = dev;
> 			goto done;
> 		}
> 	}
>-	ret = -ENODEV;
>+
>+	if (CONFIG_IS_ENABLED(FALLBACK_DRIVERS) && uc->uc_drv->fallback_drv_name)
>+		ret = uclass_bind_fallback(uc, node, devp);
>+	else
>+		ret = -ENODEV;
> 
> done:
> 	log(LOGC_DM, LOGL_DEBUG, "   - result for %s: %s (ret=%d)\n",
> 	    ofnode_get_name(node), *devp ? (*devp)->name : "(none)", ret);
>diff --git a/include/dm/uclass.h b/include/dm/uclass.h
>index 456eef7f2f31..b99e36485bc5 100644
>--- a/include/dm/uclass.h
>+++ b/include/dm/uclass.h
>@@ -67,8 +67,10 @@ struct udevice;
>  * @child_pre_probe: Called before a child in this uclass is probed
>  * @child_post_probe: Called after a child in this uclass is probed
>  * @init: Called to set up the uclass
>  * @destroy: Called to destroy the uclass
>+ * @stub_drv_name: Name of a stub driver to use for devices that are not
>+ * supported by any other driver.
>  * @priv_auto: If non-zero this is the size of the private data
>  * to be allocated in the uclass's ->priv pointer. If zero, then the uclass
>  * driver is responsible for allocating any data required.
>  * @per_device_auto: Each device can hold private data owned
>@@ -98,8 +100,9 @@ struct uclass_driver {
> 	int (*child_pre_probe)(struct udevice *dev);
> 	int (*child_post_probe)(struct udevice *dev);
> 	int (*init)(struct uclass *class);
> 	int (*destroy)(struct uclass *class);
>+	const char *fallback_drv_name;
> 	int priv_auto;
> 	int per_device_auto;
> 	int per_device_plat_auto;
> 	int per_child_auto;
>