On Fri, Jan 20, 2017 at 08:03:33AM +0100, Thierry Reding wrote: > On Thu, Jan 19, 2017 at 06:58:30PM +0100, Hans de Goede wrote: > > The primary consumer of the lpss pwm is the i915 kms driver, > > the i915 driver does not support get_pwm returning -EPROBE_DEFER and > > its init is very complex making this is almost impossible to fix. > > > > This commit changes the PWM_LPSS Kconfig from a tristate to a bool, so > > that when the i915 driver loads the lpss pwm will be available avoiding > > the -EPROBE_DEFER issue. Note that this is identical to how the same > > problem was solved for the pwm-crc driver, which is used by the i915 > > driver on other platforms. > > > > Signed-off-by: Hans de Goede <hdego...@redhat.com> > > Acked-by: Jani Nikula <jani.nik...@intel.com> > > --- > > Changes in v2: > > -Drop the pwm_add_table call (this has been moved to the acpi_lpss driver) > > --- > > drivers/pwm/Kconfig | 12 +++--------- > > 1 file changed, 3 insertions(+), 9 deletions(-) > > For the record I think this is completely wrong and i915 should be > taught how to deal with -EPROBE_DEFER. We've gone through a lot of > pain to clean up this kind of init-level ordering on other devices > and the result is, in my opinion, a *lot* better than what we had > before. It'd be shame to see i915 backpedal on that.
Looking into i915 a little, I don't see why handling -EPROBE_DEFER would
be very complicated. The call stack looks somewhat like this:
i915_pci_probe()
i915_driver_load()
i915_load_modeset_init()
intel_modeset_init()
intel_setup_outputs()
intel_dsi_init()
intel_panel_setup_backlight()
pwm_setup_backlight()
In the above, intel_modeset_init() is the last one that propagates
errors, but its caller, i915_load_modeset_init() properly handles
failure from other function calls. Also, pwm_setup_backlight() can
return errors to intel_panel_setup_backlight(), which will in turn
propagate them to intel_dsi_init().
So I'd think that in order to properly handle -EPROBE_DEFER you'd only
need to propagate errors back up this way:
intel_panel_setup_backlight()
intel_dsi_init()
intel_setup_outputs()
intel_modeset_init()
That seems to me to be far from "almost impossible".
Thierry
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