Hi,
On 20-01-17 08:18, Thierry Reding wrote:
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 <hdegoede@xxxxxxxxxx>
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>
---
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".
I will let the i915 devs answer this.
IIRC a lot of setup is already done at this point, including some changes
to the hw and we really do not want to change the init-sequence, or
repeat parts of it.
I myself was actually thinking about solving this by figuring out if the
pwm is necessary and getting it early on, but the figuring out bit is non
trivial.
Anyways as said I will let the i915 devs answer this.
Regards,
Hans
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