On Thu, Jun 23, 2022 at 10:36 AM Ahmad Fatoum <a.fat...@pengutronix.de> wrote: > > Hello Saravana, > > On 23.06.22 19:26, Saravana Kannan wrote: > > On Thu, Jun 23, 2022 at 3:05 AM sascha hauer <s...@pengutronix.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 <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. > > > > 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. > > I have a system that doesn't use stdout-path and has the bootloader > set console= either to ttynull when secure booting or to an UART > when booting normally. How would I optimize the kernel to avoid > my UART being loaded after DMA controller probe without touching > the bootloader? >
Thanks for the report Ahmad. I think someone else reported a similar thing in another thread. I plan to take a look at it. It should be possible to find the device and set the flag for those devices too. -Saravana _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu