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? Cheers, Ahmad > > -Saravana > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ iommu mailing list email@example.com https://lists.linuxfoundation.org/mailman/listinfo/iommu