Re: [PATCH v1] drm/i915/bxt: use NULL for GPIO connection ID

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: "Jani Nikula" <jani.nikula@intel.com>,
	"David Airlie" <airlied@linux.ie>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>
Subject: Re: [PATCH v1] drm/i915/bxt: use NULL for GPIO connection ID
Date: Tue, 21 Feb 2017 18:52:24 +0200	[thread overview]
Message-ID: <1487695944.20145.15.camel@linux.intel.com> (raw)
In-Reply-To: <87h93njyrx.fsf@intel.com>

On Tue, 2017-02-21 at 18:26 +0200, Jani Nikula wrote:
> On Tue, 21 Feb 2017, Andy Shevchenko <andriy.shevchenko@linux.intel.co
> m> wrote:
> > The commit 213e08ad60ba ("drm/i915/bxt: add bxt dsi gpio element
> > support") enables GPIO support for Broxton based platforms.
> > 
> > While using that API we might get into troubles in the future,
> > because
> > we can't rely on label "panel" in the driver since vendor firmware
> > might
> > provide any GPIO pin there, e.g. "reset", and even mark it in _DSD
> > (in
> > which case the request will fail).
> > 
> > To avoid inconsistency and potential issues we have two options:
> > a) generate GPIO ACPI mapping table and supply it via
> > acpi_dev_add_driver_gpios(), or
> > b) just pass NULL as connection ID.
> > 
> > The b) approach is much simplier and would work since the driver
> > relies
> > on GPIO indeces only. Moreover, the _CRS fallback mechanism, when
> > requesting GPIO, is going to be stricter, and supplying non-NULL
> > connection ID when neither _DSD, nor GPIO ACPI mapping is present,
> > will
> > make request fail.
> 
> The patch version log in the commit suggests otherwise; we'd tried and
> failed with NULL,

Can I see DSDT excerpts of the platform that fails?

>  until Mika realized passing "panel" works:
> 
>     v2 by Mika: switch *NULL* to *"panel"* when requesting gpio for
> MIPI/DSI
>     panel.

> 
> See also [1]. What has changed since then that should make this work
> now? We shouldn't apply until we get Tested-by's.

Not changed yet, but *going to be*. See my repository here [2].
To fix the mess with GPIO ACPI stuff we are going to make request
stricter as I pointed in commit message above, i.e. asking for a GPIO by
connection ID without _DSD present will guarantee -ENOENT since it will
be no fallback to _CRS. You may follow discussion in our internal
mailing list for drivers.

> [1] http://mid.mail-archive.com/1480597671.26172.82.camel@intel.com

[2] http://bitbucket.org/andy-shev/linux/branch/topic%2Fuart%2frpm

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
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