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Date: Thu, 23 Jun 2022 10:26:46 -0700 From: Saravana Kannan <saravanak@...gle.com> To: sascha hauer <sha@...gutronix.de> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Rob Herring <robh+dt@...nel.org>, Frank Rowand <frowand.list@...il.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Daniel Scally <djrscally@...il.com>, Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Sakari Ailus <sakari.ailus@...ux.intel.com>, Len Brown <lenb@...nel.org>, peng fan <peng.fan@....com>, kevin hilman <khilman@...nel.org>, ulf hansson <ulf.hansson@...aro.org>, len brown <len.brown@...el.com>, pavel machek <pavel@....cz>, joerg roedel <joro@...tes.org>, will deacon <will@...nel.org>, andrew lunn <andrew@...n.ch>, heiner kallweit <hkallweit1@...il.com>, russell king <linux@...linux.org.uk>, "david s. miller" <davem@...emloft.net>, eric dumazet <edumazet@...gle.com>, jakub kicinski <kuba@...nel.org>, paolo abeni <pabeni@...hat.com>, linus walleij <linus.walleij@...aro.org>, hideaki yoshifuji <yoshfuji@...ux-ipv6.org>, david ahern <dsahern@...nel.org>, kernel-team@...roid.com, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, iommu@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-gpio@...r.kernel.org, kernel@...gutronix.de, devicetree@...r.kernel.org, linux-acpi@...r.kernel.org Subject: Re: [PATCH v2 2/2] of: base: Avoid console probe delay when fw_devlink.strict=1 On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <sha@...gutronix.de> 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 <sha@...gutronix.de> > > Reported-by: Peng Fan <peng.fan@....com> > > Signed-off-by: Saravana Kannan <saravanak@...gle.com> > > Tested-by: Peng Fan <peng.fan@....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. That actually breaks things in a worse sense. There are cases where the consumer driver is built in and the optional supplier driver is loaded at boot. Without fw_devlink and the deferred probe timeout, we end up probing the consumer with limited functionality. With the current setup, sure we delay some probes a bit but at least everything works with the right functionality. And you can reduce or remove the delay if you want to optimize it. -Saravana
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