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

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 21 Feb 2017, Andy Shevchenko <andriy.shevchenko@linux.intel.com> 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, 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.


BR,
Jani.


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


>
> Cc: Mika Kahola <mika.kahola@intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dsi_panel_vbt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dsi_panel_vbt.c b/drivers/gpu/drm/i915/intel_dsi_panel_vbt.c
> index 8f683b8b1816..493d5ec2b53a 100644
> --- a/drivers/gpu/drm/i915/intel_dsi_panel_vbt.c
> +++ b/drivers/gpu/drm/i915/intel_dsi_panel_vbt.c
> @@ -315,7 +315,7 @@ static void bxt_exec_gpio(struct drm_i915_private *dev_priv,
>  
>  	if (!gpio_desc) {
>  		gpio_desc = devm_gpiod_get_index(dev_priv->drm.dev,
> -						 "panel", gpio_index,
> +						 NULL, gpio_index,
>  						 value ? GPIOD_OUT_LOW :
>  						 GPIOD_OUT_HIGH);

-- 
Jani Nikula, Intel Open Source Technology Center
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