Re: [PATCH 2/3] mfd: intel_soc_pmic: Rename pwm_backlight pwm-lookup to pwm_pmic_backlight

From: Hans de Goede
Date: Fri Dec 13 2019 - 07:40:47 EST


On 13-12-2019 09:27, Lee Jones wrote:
On Thu, 12 Dec 2019, Hans de Goede wrote:


On 12-12-2019 16:52, Lee Jones wrote:
On Thu, 12 Dec 2019, Hans de Goede wrote:


On 12-12-2019 09:45, Lee Jones wrote:
On Wed, 11 Dec 2019, Hans de Goede wrote:

Hi Lee,

On 10-12-2019 09:51, Lee Jones wrote:
On Tue, 19 Nov 2019, Hans de Goede wrote:

At least Bay Trail (BYT) and Cherry Trail (CHT) devices can use 1 of 2
different PWM controllers for controlling the LCD's backlight brightness.

Either the one integrated into the PMIC or the one integrated into the
SoC (the 1st LPSS PWM controller).

So far in the LPSS code on BYT we have skipped registering the LPSS PWM
controller "pwm_backlight" lookup entry when a Crystal Cove PMIC is
present, assuming that in this case the PMIC PWM controller will be used.

On CHT we have been relying on only 1 of the 2 PWM controllers being
enabled in the DSDT at the same time; and always registered the lookup.

So far this has been working, but the correct way to determine which PWM
controller needs to be used is by checking a bit in the VBT table and
recently I've learned about 2 different BYT devices:
Point of View MOBII TAB-P800W
Acer Switch 10 SW5-012

Which use a Crystal Cove PMIC, yet the LCD is connected to the SoC/LPSS
PWM controller (and the VBT correctly indicates this), so here our old
heuristics fail.

Since only the i915 driver has access to the VBT, this commit renames
the "pwm_backlight" lookup entries for the Crystal Cove PMIC's PWM
controller to "pwm_pmic_backlight" so that the i915 driver can do a
pwm_get() for the right controller depending on the VBT bit, instead of
the i915 driver relying on a "pwm_backlight" lookup getting registered
which magically points to the right controller.

Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
drivers/mfd/intel_soc_pmic_core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

For my own reference:
Acked-for-MFD-by: Lee Jones <lee.jones@xxxxxxxxxx>

As mentioned in the cover-letter, to avoid breaking bi-sectability
as well as to avoid breaking the intel-gfx CI we need to merge this series
in one go through one tree. Specifically through the drm-intel tree.
Is that ok with you ?

If this is ok with you, then you do not have to do anything, I will just push
the entire series to drm-intel. drivers/mfd/intel_soc_pmic_core.c
does not see much changes so I do not expect this to lead to any conflicts.

It's fine, so long as a minimal immutable pull-request is provided.
Whether it's pulled or not will depend on a number of factors, but it
needs to be an option.

The way the drm subsys works that is not really a readily available
option. The struct definition which this patch changes a single line in
has not been touched since 2015-06-26 so I really doubt we will get a
conflict from this.

Always with the exceptions ...

OOI, why does this *have* to go through the DRM tree?

This patch renames the name used to lookup the pwm controller from
"pwm_backlight" to "pwm_pmic_backlight" because there are 2 possible
pwm controllers which may be used, one in the SoC itself and one
in the PMIC. Which controller should be used is described in a table
in the Video BIOS, so another part of this series adds this code to
the i915 driver:

- panel->backlight.pwm = pwm_get(dev->dev, "pwm_backlight");
+ /* Get the right PWM chip for DSI backlight according to VBT */
+ if (dev_priv->vbt.dsi.config->pwm_blc == PPS_BLC_PMIC) {
+ panel->backlight.pwm = pwm_get(dev->dev, "pwm_pmic_backlight");
+ desc = "PMIC";
+ } else {
+ panel->backlight.pwm = pwm_get(dev->dev, "pwm_soc_backlight");
+ desc = "SoC";
+ }

So both not to break bisectability, but also so as to not break the extensive
CI system which is used to test the i915 driver we need the MFD change doing
the rename to go upstrream through the same tree as the i915 change.

I have even considered just squashing the 2 commits together as having only 1
present, but not the other breaks stuff left and right.

That doesn't answer the question.

Why do they all *have* to go in via the DRM tree specifically?

1. As explained these chanegs need to stay together
2. This change is primarily a drm/i915 change. Also the i915 code sees lots
of changes every cycle, where as the change to the mfd code touches a block
of code which has not been touched since 2015-06-26, so the chance of conflicts
is much bigger if this goes on through another tree.

I honestly do not see the problem here? Let me reverse the question why should this
NOT go in through the drm tree?