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From: Luca Ceresoli <luca.ceresoli@bootlin.com>
To: Maxime Ripard <mripard@kernel.org>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Robert Foss <rfoss@kernel.org>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
	Miguel Ojeda <ojeda@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>,
	Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>,
	Chaoyi Chen <chaoyi.chen@rock-chips.com>,
	Hui Pu <Hui.Pu@gehealthcare.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	llvm@lists.linux.dev
Subject: Re: [PATCH v2 3/9] drm/bridge: add drm_for_each_bridge_in_chain_scoped()
Date: Wed, 20 Aug 2025 11:40:30 +0200	[thread overview]
Message-ID: <20250820114030.401e5d4f@booty> (raw)
In-Reply-To: <20250819180137.28ca89c0@booty>

Hi Maxime,

On Tue, 19 Aug 2025 18:01:37 +0200
Luca Ceresoli <luca.ceresoli@bootlin.com> wrote:

> Hi Maxime,
> 
> On Tue, 19 Aug 2025 15:47:06 +0200
> Maxime Ripard <mripard@kernel.org> wrote:
> 
> > > +/**
> > > + * drm_for_each_bridge_in_chain_scoped - iterate over all bridges attached
> > > + *                                       to an encoder
> > > + * @encoder: the encoder to iterate bridges on
> > > + * @bridge: a bridge pointer updated to point to the current bridge at each
> > > + *	    iteration
> > > + *
> > > + * Iterate over all bridges present in the bridge chain attached to @encoder.
> > > + *
> > > + * Automatically gets/puts the bridge reference while iterating, and puts
> > > + * the reference even if returning or breaking in the middle of the loop.
> > > + */
> > > +#define drm_for_each_bridge_in_chain_scoped(encoder, bridge)		\
> > > +	for (struct drm_bridge *bridge __free(drm_bridge_put) =		\
> > > +	     drm_bridge_chain_get_first_bridge(encoder);		\    
> > 
> > So my understanding is that the initial value of bridge would be cleaned
> > up with drm_bridge_put...
> >   
> > > +	     bridge;							\
> > > +	     bridge = drm_bridge_get_next_bridge_and_put(bridge))    
> > 
> > ... but also when iterating?
> > 
> > So if we have more than 0 values, we put two references?  
> 
> No, this is not the case. The __free action is executed only when
> exiting the entire for loop, not a single iteration.
> 
> This is consistent with the fact that the loop variable is persistent
> across iterations.

PS: here's the C language spec reference:

> 6.8.5.3 The for statement
> The statement
> for ( clause-1 ; expression-2 ; expression-3 ) statement
> behaves as follows:
> [...]
> If clause-1 is a declaration, the scope of any identifiers it declares
> is the remainder of the declaration and the entire loop 

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
https://rgambord.github.io/c99-doc/sections/6/8/5/3/index.html

Best regards,
Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

  reply	other threads:[~2025-08-20  9:40 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-08-08 14:49 [PATCH v2 0/9] drm/bridge: get/put the bridge when looping over the encoder chain Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 1/9] drm/display: bridge-connector: use scope-specific variable for the bridge pointer Luca Ceresoli
2025-08-19 13:43   ` Maxime Ripard
2025-08-08 14:49 ` [PATCH v2 2/9] drm/display: bridge-connector: remove unused variable assignment Luca Ceresoli
2025-08-19 13:43   ` Maxime Ripard
2025-08-08 14:49 ` [PATCH v2 3/9] drm/bridge: add drm_for_each_bridge_in_chain_scoped() Luca Ceresoli
2025-08-19 13:47   ` Maxime Ripard
2025-08-19 16:01     ` Luca Ceresoli
2025-08-20  9:40       ` Luca Ceresoli [this message]
2025-09-02 21:53         ` Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 4/9] drm/display: bridge-connector: use drm_for_each_bridge_in_chain_scoped() Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 5/9] drm/atomic: " Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 6/9] drm/bridge: " Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 7/9] drm/bridge: remove drm_for_each_bridge_in_chain() Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 8/9] drm/bridge: add drm_for_each_bridge_in_chain_from() Luca Ceresoli
2025-08-08 14:49 ` [PATCH v2 9/9] drm/omap: use drm_for_each_bridge_in_chain_from() Luca Ceresoli
2025-08-19 10:15 ` [PATCH v2 0/9] drm/bridge: get/put the bridge when looping over the encoder chain Luca Ceresoli
2025-09-05 13:54 ` (subset) " Luca Ceresoli

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