Re: [PATCH v2 6/9] Revert "driver core: Set default deferred_probe_timeout back to 0."

Geert Uytterhoeven
2022-07-20T17:37:25Z

Hi Saravana,

On Wed, Jun 1, 2022 at 9:45 AM Saravana Kannan <saravanak@google.com> wrote:
> This reverts commit 11f7e7ef553b6b93ac1aa74a3c2011b9cc8aeb61.
>
> Let's take another shot at getting deferred_probe_timeout=10 to work.
>
> Signed-off-by: Saravana Kannan <saravanak@google.com>

Thanks for your patch, which is now commit f516d01b9df2782b
("Revert "driver core: Set default deferred_probe_timeout
back to 0."") in driver-core/driver-core-next.

Wolfram found an issue on a Renesas board where disabling the IOMMU
driver (CONFIG_IPMMU_VMSA=n) causes the system to fail to boot,
and bisected this to a merge of driver-core/driver-core-next.
After some trials, I managed to reproduce the issue, and bisected it
further to commit f516d01b9df2782b.

The affected config has:
CONFIG_MODULES=y
CONFIG_RCAR_DMAC=y
CONFIG_IPMMU_VMSA=n

In arch/arm64/boot/dts/renesas/r8a77951-salvator-xs.dtb,
e6e88000.serial links to a dmac, and the dmac links to an iommu,
for which no driver is available.

Playing with deferred_probe_timeout values doesn't help.

However, the above options do not seem to be sufficient to trigger
the issue, as I had other configs with those three options that do
boot fine.

After bisecting configs, I found the culprit: CONFIG_IP_PNP.
As Wolfram was using an initramfs, CONFIG_IP_PNP was not needed.
If CONFIG_IP_PNP=n, booting fails.
If CONFIG_IP_PNP=y, booting succeeds.
In fact, just disabling late_initcall(ip_auto_config) makes it fail,
too.
Reducing ip_auto_config(), it turns out the call to
wait_for_init_devices_probe() is what is needed to unblock booting.

So I guess wait_for_init_devices_probe() needs to be called (where?)
if CONFIG_IP_PNP=n, too?

> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -256,7 +256,12 @@ static int deferred_devs_show(struct seq_file *s, void *data)
> }
> DEFINE_SHOW_ATTRIBUTE(deferred_devs);
>
> +#ifdef CONFIG_MODULES
> +int driver_deferred_probe_timeout = 10;
> +#else
> int driver_deferred_probe_timeout;
> +#endif
> +
> EXPORT_SYMBOL_GPL(driver_deferred_probe_timeout);
>
> static int __init deferred_probe_timeout_setup(char *str)

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds