Re: [Intel-gfx] [PATCH v1] drm/i915/dsi: Drop double check for ACPI companion device

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, May 29, 2020 at 03:33:17PM +0300, Andy Shevchenko wrote:
> acpi_dev_get_resources() does perform the NULL pointer check against
> ACPI companion device which is given as function parameter. Thus,
> there is no need to duplicate this check in the caller.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Sorry, I did look at this but apparently forgot to reply...

> ---
>  drivers/gpu/drm/i915/display/intel_dsi_vbt.c | 24 ++++++++------------
>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dsi_vbt.c b/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
> index 574dcfec9577..6f9e08cda964 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsi_vbt.c
> @@ -426,23 +426,19 @@ static void i2c_acpi_find_adapter(struct intel_dsi *intel_dsi,
>  {
>  	struct drm_device *drm_dev = intel_dsi->base.base.dev;
>  	struct device *dev = &drm_dev->pdev->dev;
> -	struct acpi_device *acpi_dev;
> +	struct acpi_device *acpi_dev = ACPI_COMPANION(dev);
>  	struct list_head resource_list;
>  	struct i2c_adapter_lookup lookup;
>  
> -	acpi_dev = ACPI_COMPANION(dev);
> -	if (acpi_dev) {
> -		memset(&lookup, 0, sizeof(lookup));
> -		lookup.slave_addr = slave_addr;
> -		lookup.intel_dsi = intel_dsi;
> -		lookup.dev_handle = acpi_device_handle(acpi_dev);
> -
> -		INIT_LIST_HEAD(&resource_list);
> -		acpi_dev_get_resources(acpi_dev, &resource_list,
> -				       i2c_adapter_lookup,
> -				       &lookup);
> -		acpi_dev_free_resource_list(&resource_list);
> -	}
> +	memset(&lookup, 0, sizeof(lookup));
> +	lookup.slave_addr = slave_addr;
> +	lookup.intel_dsi = intel_dsi;
> +	lookup.dev_handle = acpi_device_handle(acpi_dev);

struct i2c_adapter_lookup lookup = {
	.slave_addr = ...
};

?

> +
> +	INIT_LIST_HEAD(&resource_list);

Declare as LIST_HEAD(resource_list); ?

> +	acpi_dev_get_resources(acpi_dev, &resource_list,
> +			       i2c_adapter_lookup, &lookup);
> +	acpi_dev_free_resource_list(&resource_list);

I was very confused by this code since on the first glance it appears to
absolutely nothing. After a deeper look it looks like
i2c_adapter_lookup() magically mutates intel_dsi->i2c_bus_num.
Did I mention I hate functions with side effects? IMO would be much
better if i2c_adapter_lookup() did what it says on the tin and just
returned the adapter number and let the caller deal with it. But
this is a pre-existing issue with the code and so not directly related
to your patch.

>  }
>  #else
>  static inline void i2c_acpi_find_adapter(struct intel_dsi *intel_dsi,
> -- 
> 2.26.2
> 
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
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-- 
Ville Syrjälä
Intel
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