Hi,
On 05-12-16 11:59, Thierry Reding wrote:
On Mon, Dec 05, 2016 at 09:18:03AM +0100, Hans de Goede wrote:
Hi,
On 05-12-16 08:46, Thierry Reding wrote:
On Fri, Dec 02, 2016 at 11:17:35AM +0100, Hans de Goede wrote:
The primary consumer of the lpss pwm is the i915 kms driver, but
currently that driver cannot get the pwm because i915 platforms are
not using devicetree and pwm-lpss does not call pwm_add_table.
Another problem is that i915 does not support get_pwm returning
-EPROBE_DEFER and i915's init is very complex and 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.
Being builtin also allows calling pwm_add_table directly from the
pwm-lpss code, otherwise the pwm_add_table call would need to be put
somewhere else to ensure it happens before i915 calls pwm_get,
even if i915 would support -EPROBE_DEFER.
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
drivers/pwm/Kconfig | 12 +++---------
drivers/pwm/pwm-lpss.c | 11 +++++++++++
2 files changed, 14 insertions(+), 9 deletions(-)
This is completely backwards. You're putting board-specific bits into a
generic driver.
This is not really board specific I'm advertising that the goal of
the pwm is to be used to control a backlight.
pwm_add_table() is a board-specific API. Documentation/pwm.txt says that
"board setup code" should be using pwm_add_table(). Using it from within
the provider is completely the opposite.
The problem here really is that there is no such thing as
board setup code on x86 + EFI/ACPI, that is supposedly all
handled by the EFI/ACPI code there.
Before typing this reply I've been thinking about another place
to put the pwm_add_table call put I cannot come up with any.
I suggested drivers/platform/x86. A bunch of code in there is doing
exactly the kind of board/platform setup stuff that you're trying to do
here.
All drivers under drivers/platform/x86 bind to something, be it
an ACPI interface or an actual platform device. In the case of the
pwm-lpss we have an actual platform or pci device and a driver binding
to it, that is the only common code path I see where I can add the
pwm_add_table.
Sure I can put a built-in bit of code under drivers/platform/x86
which checks from its module_init() that there is an pwm-lpss controller
present (either listed under ACPI or through PCI) and then calls
pwm_add_table, but seems silly. Note as said this then must be
built-in, because if it is a module nothing will trigger the
loading of the module, unless I add duplicate MODULE_DEVICE_TABLE
tables in there with the code under drivers/pwm/pwm-lpss.
TL;DR: the problem is that something needs to trigger / activate
the code doing the pwm_add_table() and AFAICT we have no other
trigger then the presence of the pwm-lpss device, at which point
the pwm_lpss_probe function becomes the best place to do the
pwm_add_table call.
Regards,
Hans
drivers/acpi/acpi_lpss.c comes to mind, but that would only work
with the pwm device in acpi mode and not with it in pci mode.
Another candidate would be to put the pwm_add_table call in the
i915 driver itself, when the vbt says we need to use an external
pwm and the plaform is cherrytrail, but it does not know if the
pwm device is in pci or acpi modes which requires a different
provider entry in the table.
i915 isn't a good location for that either. This should really be driven
by code external to any generic drivers. It's exactly the kind of glue
that platform or board setup code is used for.
If you look at drivers/platform/x86/intel_oaktrail.c, it does very
similar things. If this is specific to Cherry Trail, I'm sure you can
find ways to identify the platform as such and drive it in a similar way
from drivers/platform/x86/intel_cherrytrail.c.
Besides that having the pwm in the table will not do anything
unless the i915 driver does a pwm_get, so this does not gain us
anything.
It will keep the driver generic and put the board code where it belongs.
I call that very much of a gain.
Maybe we need to rename the con_id from "pwm_backlight" to
"pwm_lpss0", that way it is very clear which pwm any pwm_get calls
are getting (and lpss-pwm.c is obviously the correct place to
do the add_table), and then we can teach the i915 code to look
for "pwm_lpss0" based on vbt info ?
pwm_backlight is the much better consumer name because by your own words
that's exactly what the PWM is used for. Obfuscating this by turning the
name into something unrecognizable such as pwm_lpss0 isn't going to
change any of the above.
Thierry
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