Hi Rob, Thank you for taking the time to check our patch and provide valuable feedback. We appreciate your comments/suggestions. Please find our reply to your comments. On Thu, Sep 12, 2024 at 03:46:34PM -0500, Rob Herring wrote: > On Wed, Sep 11, 2024 at 07:53:19PM +0530, Nayeemahmed Badebade wrote: > > Probe control driver framework allows deferring the probes of a group of > > devices to an arbitrary time, giving the user control to trigger the probes > > after boot. This is useful for deferring probes from builtin drivers that > > are not required during boot and probe when user wants after boot. > > This seems like the wrong way around to me. Why not define what you want > to probe first or some priority order? I could see use for kernel to > probe whatever is the console device first. Or the rootfs device... You > don't need anything added to DT for those. > > Of course, there's the issue that Linux probes are triggered bottom-up > rather than top-down. > Our intention is to only postpone some driver probes not required during boot, similar to https://elinux.org/Deferred_Initcalls. But instead of delaying initcall execution(which requires initmem to be kept and not freed during boot) we are trying to delay driver probes as this is much simpler. > > > This is achieved by adding a dummy device aka probe control device node > > as provider to a group of devices(consumer nodes) in platform's device > > tree. Consumers are the devices we want to probe after boot. > > There's the obvious question of then why not make those devices modules > instead of built-in? > Yes we can use modules for this, but there are drivers that cannot be built as modules and this framework is specifically for such scenario. Example: drivers/pci/controller/dwc/pci-imx6.c > > > > To establish control over consumer device probes, each consumer device node > > need to refer the probe control provider node by the phandle. > > 'probe-control-supply' property is used for this. > > > > Example: > > // The node below defines a probe control device/provider node > > prb_ctrl_dev_0: prb_ctrl_dev_0 { > > compatible = "linux,probe-control"; > > }; > > > > // The node below is the consumer device node that refers to provider > > // node by its phandle and a result will not be probed until provider > > // node is probed. > > pcie@1ffc000 { > > reg = <0x01ffc000 0x04000>, <0x01f00000 0x80000>; > > #address-cells = <3>; > > #size-cells = <2>; > > device_type = "pci"; > > ranges = <0x81000000 0 0 0x01f80000 0 0x00010000>, > > <0x82000000 0 0x01000000 0x01000000 0 0x00f00000>; > > > > probe-control-supply = <&prb_ctrl_dev_0>; > > }; > > Sorry, but this isn't going to happen in DT. > You mean we cannot add custom properties like this to an existing device node in DT? > > > > fw_devlink ensures consumers are not probed until provider is probed > > successfully. The provider probe during boot returns -ENXIO and is not > > re-probed again. > > > > The driver provides debug interface /sys/kernel/debug/probe_control_status > > for checking probe control status of registered probe control devices. > > # cat /sys/kernel/debug/probe_control_status > > prb_ctrl_dev_0: [not triggered] > > Consumers: 1ffc000.pcie > > > > Interface /sys/kernel/probe_control/trigger is provided for triggering > > probes of the probe control devices. User can write to this interface to > > trigger specific or all device probes managed by this driver. > > Once the probe is triggered by user, provider probe control device is added > > to deferred_probe_pending_list and driver_deferred_probe_trigger() is > > triggered. This time the probe of probe control device will be > > successful and its consumers will then be probed. > > > > To trigger specific provider probe: > > # echo prb_ctrl_dev_0 > /sys/kernel/probe_control/trigger > > > > To trigger all registered provider probes > > # echo all > /sys/kernel/probe_control/trigger > > > > Signed-off-by: Toyama Yoshihiro <yoshihiro.toyama@xxxxxxxx> > > Signed-off-by: Nayeemahmed Badebade <nayeemahmed.badebade@xxxxxxxx> > > This is wrong. Either Toyama is the author and you need to fix the git > author, or you both are authors and you need a Co-developed-by tag for > Toyama. Sorry about that, we will fix this. Thanks, Nayeem
