Re: [PATCH v2] driver: core: Allow subsystems to continue deferring probe

[Rob Herring <robh@xxxxxxxxxx>]

On Thu, Jun 13, 2019 at 11:00 AM Thierry Reding
<thierry.reding@xxxxxxxxx> wrote:
>
> From: Thierry Reding <treding@xxxxxxxxxx>
>
> Some subsystems, such as pinctrl, allow continuing to defer probe
> indefinitely. This is useful for devices that depend on resources
> provided by devices that are only probed after the init stage.
>
> One example of this can be seen on Tegra, where the DPAUX hardware
> contains pinmuxing controls for pins that it shares with an I2C
> controller. The I2C controller is typically used for communication
> with a monitor over HDMI (DDC). However, other instances of the I2C
> controller are used to access system critical components, such as a
> PMIC. The I2C controller driver will therefore usually be a builtin
> driver, whereas the DPAUX driver is part of the display driver that
> is loaded from a module to avoid bloating the kernel image with all
> of the DRM/KMS subsystem.
>
> In this particular case the pins used by this I2C/DDC controller
> become accessible very late in the boot process. However, since the
> controller is only used in conjunction with display, that's not an
> issue.
>
> Unfortunately the driver core currently outputs a warning message
> when a device fails to get the pinctrl before the end of the init
> stage. That can be confusing for the user because it may sound like
> an unwanted error occurred, whereas it's really an expected and
> harmless situation.
>
> In order to eliminate this warning, this patch allows callers of the
> driver_deferred_probe_check_state() helper to specify that they want
> to continue deferring probe, regardless of whether we're past the
> init stage or not. All of the callers of that function are updated
> for the new signature, but only the pinctrl subsystem passes a true
> value in the new persist parameter if appropriate.
>
> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
> ---
> Changes in v2:
> - pass persist flag via flags parameter to make the function call easier
>   to understand
>
>  drivers/base/dd.c            | 19 ++++++++++++++-----
>  drivers/base/power/domain.c  |  2 +-
>  drivers/iommu/of_iommu.c     |  2 +-
>  drivers/pinctrl/devicetree.c |  9 +++++----
>  include/linux/device.h       | 18 +++++++++++++++++-
>  5 files changed, 38 insertions(+), 12 deletions(-)

Acked-by: Rob Herring <robh@xxxxxxxxxx>