Re: [PATCH] drm/i915/backlight: Remove a useless kstrdup_const()

[Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>]

Le 30/09/2024 à 09:48, Jani Nikula a écrit :
> On Sat, 28 Sep 2024, Christophe JAILLET <christophe.jaillet@xxxxxxxxxx> wrote:
> > "name" is allocated and freed in intel_backlight_device_register().
> > The initial allocation just duplicates "intel_backlight".
> >
> > Later, if a device with this name has already been registered, another
> > dynamically generated one is allocated using kasprintf().
> >
> > So at the end of the function, when "name" is freed, it can point either to
> > the initial static literal "intel_backlight" or to the kasprintf()'ed one.
> >
> > So kfree_const() is used.
> >
> > However, when built as a module, kstrdup_const() and kfree_const() don't
> > work as one would expect and are just plain kstrdup() and kfree().
> >
> >
> > Slightly change the logic and introduce a new variable to hold the
> > address returned by kasprintf() should it be used.
> >
> > This saves a memory allocation/free and avoids these _const functions,
> > which names can be confusing when used with code built as module.
>
> Okay, I'd rather revert your earlier commit 379b63e7e682
> ("drm/i915/display: Save a few bytes of memory in
> intel_backlight_device_register()") than add this.

Hi,

that works for me. Thanks and sorry for the noise.

CJ

> The code simplicity is much more important than saving a few bytes.
>
> BR,
> Jani.
>
>
>
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > ---
> > Compile tested only.
> >
> > For the records, this patch is a clean-up effort related to discussions at:
> >    - https://lore.kernel.org/all/ZvHurCYlCoi1ZTCX@skv.local/
> >    - https://lore.kernel.org/all/20240924050937.697118-1-senozhatsky@xxxxxxxxxxxx/
> > ---
> >   drivers/gpu/drm/i915/display/intel_backlight.c | 17 +++++++----------
> >   1 file changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
> > index 9e05745d797d..bf7686aa044f 100644
> > --- a/drivers/gpu/drm/i915/display/intel_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_backlight.c
> > @@ -914,9 +914,9 @@ int intel_backlight_device_register(struct intel_connector *connector)
> >   {
> >   	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> >   	struct intel_panel *panel = &connector->panel;
> > +	const char *name, *new_name = NULL;
> >   	struct backlight_properties props;
> >   	struct backlight_device *bd;
> > -	const char *name;
> >   	int ret = 0;
> >   
> >   	if (WARN_ON(panel->backlight.device))
> > @@ -949,10 +949,7 @@ int intel_backlight_device_register(struct intel_connector *connector)
> >   	else
> >   		props.power = BACKLIGHT_POWER_OFF;
> >   
> > -	name = kstrdup_const("intel_backlight", GFP_KERNEL);
> > -	if (!name)
> > -		return -ENOMEM;
> > -
> > +	name = "intel_backlight";
> >   	bd = backlight_device_get_by_name(name);
> >   	if (bd) {
> >   		put_device(&bd->dev);
> > @@ -963,11 +960,11 @@ int intel_backlight_device_register(struct intel_connector *connector)
> >   		 * compatibility. Use unique names for subsequent backlight devices as a
> >   		 * fallback when the default name already exists.
> >   		 */
> > -		kfree_const(name);
> > -		name = kasprintf(GFP_KERNEL, "card%d-%s-backlight",
> > -				 i915->drm.primary->index, connector->base.name);
> > -		if (!name)
> > +		new_name = kasprintf(GFP_KERNEL, "card%d-%s-backlight",
> > +				     i915->drm.primary->index, connector->base.name);
> > +		if (!new_name)
> >   			return -ENOMEM;
> > +		name = new_name;
> >   	}
> >   	bd = backlight_device_register(name, connector->base.kdev, connector,
> >   				       &intel_backlight_device_ops, &props);
> > @@ -987,7 +984,7 @@ int intel_backlight_device_register(struct intel_connector *connector)
> >   		    connector->base.base.id, connector->base.name, name);
> >   
> >   out:
> > -	kfree_const(name);
> > +	kfree(new_name);
> >   
> >   	return ret;
> >   }