Re: [PATCH v2 13/17] driver core: Use device's fwnode to check if it is waiting for suppliers

Abel Vesa
2022-06-27T11:50:53Z

On 20-11-20 18:02:28, Saravana Kannan wrote:
> To check if a device is still waiting for its supplier devices to be
> added, we used to check if the devices is in a global
> waiting_for_suppliers list. Since the global list will be deleted in
> subsequent patches, this patch stops using this check.
>
> Instead, this patch uses a more device specific check. It checks if the
> device's fwnode has any fwnode links that haven't been converted to
> device links yet.
>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
> drivers/base/core.c | 18 ++++++++----------
> 1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 395dece1c83a..1873cecb0cc4 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -51,6 +51,7 @@ static DEFINE_MUTEX(wfs_lock);
> static LIST_HEAD(deferred_sync);
> static unsigned int defer_sync_state_count = 1;
> static DEFINE_MUTEX(fwnode_link_lock);
> +static bool fw_devlink_is_permissive(void);
>
> /**
> * fwnode_link_add - Create a link between two fwnode_handles.
> @@ -995,13 +996,13 @@ int device_links_check_suppliers(struct device *dev)
> * Device waiting for supplier to become available is not allowed to
> * probe.
> */
> - mutex_lock(&wfs_lock);
> - if (!list_empty(&dev->links.needs_suppliers) &&
> - dev->links.need_for_probe) {
> - mutex_unlock(&wfs_lock);
> + mutex_lock(&fwnode_link_lock);
> + if (dev->fwnode && !list_empty(&dev->fwnode->suppliers) &&
> + !fw_devlink_is_permissive()) {
> + mutex_unlock(&fwnode_link_lock);

Hi Saravana,

First of, sorry for going back to this.

There is a scenario where this check will not work and probably should
work. It goes like this:

A clock controller is not allowed to probe because it uses a clock from a child device of a
consumer, like so:

dispcc: clock-controller@af00000 {
clocks = <&dsi0_phy 0>;
};

mdss: mdss@ae00000 {
clocks = <&dispcc DISP_CC_MDSS_MDP_CLK>;

dsi0_phy: dsi-phy@ae94400 {
clocks = <&dispcc DISP_CC_MDSS_AHB_CLK>,
};
};

This is a real scenario actually, but I stripped it down to the essentials.

So, the dsi0_phy will be "device_add'ed" (through of_platform_populate) by the mdss probe.
The mdss will probe defer waiting for the DISP_CC_MDSS_MDP_CLK, while
the dispcc will probe defer waiting for the dsi0_phy (supplier).

Basically, this 'supplier availability check' does not work when a supplier might
be populated by a consumer of the device that is currently trying to probe.

Abel

> return -EPROBE_DEFER;
> }
> - mutex_unlock(&wfs_lock);
> + mutex_unlock(&fwnode_link_lock);
>
> device_links_write_lock();
>
> @@ -1167,10 +1168,7 @@ static ssize_t waiting_for_supplier_show(struct device *dev,
> bool val;
>
> device_lock(dev);
> - mutex_lock(&wfs_lock);
> - val = !list_empty(&dev->links.needs_suppliers)
> - && dev->links.need_for_probe;
> - mutex_unlock(&wfs_lock);
> + val = !list_empty(&dev->fwnode->suppliers);
> device_unlock(dev);
> return sysfs_emit(buf, "%u\n", val);
> }
> @@ -2202,7 +2200,7 @@ static int device_add_attrs(struct device *dev)
> goto err_remove_dev_groups;
> }
>
> - if (fw_devlink_flags && !fw_devlink_is_permissive()) {
> + if (fw_devlink_flags && !fw_devlink_is_permissive() && dev->fwnode) {
> error = device_create_file(dev, &dev_attr_waiting_for_supplier);
> if (error)
> goto err_remove_dev_online;
> --
> 2.29.2.454.gaff20da3a2-goog
>
>