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Date:   Fri, 13 Dec 2019 08:27:34 +0000
From:   Lee Jones <lee.jones@linaro.org>
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Ville =?iso-8859-1?Q?Syrj=E4l=E4?= 
        <ville.syrjala@linux.intel.com>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-acpi@vger.kernel.org,
        intel-gfx <intel-gfx@lists.freedesktop.org>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] mfd: intel_soc_pmic: Rename pwm_backlight pwm-lookup
 to pwm_pmic_backlight
Message-ID: <20191213082734.GE3468@dell>
References: <20191119151818.67531-1-hdegoede@redhat.com>
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On Thu, 12 Dec 2019, Hans de Goede wrote:

> 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@redhat.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@linaro.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.

That doesn't answer the question.

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

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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