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

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Date:   Thu, 12 Dec 2019 20:02:51 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-acpi@...r.kernel.org,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mfd: intel_soc_pmic: Rename pwm_backlight pwm-lookup
 to pwm_pmic_backlight

Hi,

On 12-12-2019 16:52, Lee Jones wrote:
> On Thu, 12 Dec 2019, Hans de Goede wrote:
> 
>> Hi,
>>
>> 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@...hat.com>
>>>>>> ---
>>>>>>     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@...aro.org>
>>>>
>>>> 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.

Regards,

Hans