On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote: > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote: > > Commit 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > enabled iommus and dmas dependency enforcement by default. On some > > systems, this caused the console device's probe to get delayed until the > > deferred_probe_timeout expires. > > > > We need consoles to work as soon as possible, so mark the console device > > node with FWNODE_FLAG_BEST_EFFORT so that fw_delink knows not to delay > > the probe of the console device for suppliers without drivers. The > > driver can then make the decision on where it can probe without those > > suppliers or defer its probe. > > > > Fixes: 71066545b48e ("driver core: Set fw_devlink.strict=1 by default") > > Reported-by: Sascha Hauer <s...@pengutronix.de> > > Reported-by: Peng Fan <peng....@nxp.com> > > Signed-off-by: Saravana Kannan <sarava...@google.com> > > Tested-by: Peng Fan <peng....@nxp.com> > > --- > > drivers/of/base.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/of/base.c b/drivers/of/base.c > > index d4f98c8469ed..a19cd0c73644 100644 > > --- a/drivers/of/base.c > > +++ b/drivers/of/base.c > > @@ -1919,6 +1919,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 > > align)) > > of_property_read_string(of_aliases, "stdout", &name); > > if (name) > > of_stdout = of_find_node_opts_by_path(name, > > &of_stdout_options); > > + if (of_stdout) > > + of_stdout->fwnode.flags |= FWNODE_FLAG_BEST_EFFORT; > > The device given in the stdout-path property doesn't necessarily have to > be consistent with the console= parameter. The former is usually > statically set in the device trees contained in the kernel while the > latter is dynamically set by the bootloader. So if you change the > console uart in the bootloader then you'll still run into this trap. > > It's problematic to consult only the device tree for dependencies. I > found several examples of drivers in the tree for which dma support > is optional. They use it if they can, but continue without it when > not available. "hwlock" is another property which consider several > drivers as optional. Also consider SoCs in early upstreaming phases > when the device tree is merged with "dmas" or "hwlock" properties, > but the corresponding drivers are not yet upstreamed. It's not nice > to defer probing of all these devices for a long time. > > I wonder if it wouldn't be a better approach to just probe all devices > and record the device(node) they are waiting on. Then you know that you > don't need to probe them again until the device they are waiting for > is available.
Can't we have a driver flag 'I have optional dependencies' that will trigger probe without all dependencies and then the driver can defer probe if required dependencies are not yet met. Rob _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu