Re: [PATCH 02/22] fb: atmel_lcdfb: Stop using platform_driver_probe() - Uwe Kleine-König

From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org, llvm@lists.linux.dev,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	dri-devel@lists.freedesktop.org,
	Claudiu Beznea <claudiu.beznea@tuxon.dev>,
	Nathan Chancellor <nathan@kernel.org>,
	kernel@pengutronix.de, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 02/22] fb: atmel_lcdfb: Stop using platform_driver_probe()
Date: Thu, 9 Nov 2023 11:32:34 +0100	[thread overview]
Message-ID: <20231109103234.rknpmepbhpukwbtd@pengutronix.de> (raw)
In-Reply-To: <57de52b3-201b-4599-83ba-b0a7cc8db350@gmx.de>

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Hello Helge,

On Thu, Nov 09, 2023 at 10:55:41AM +0100, Helge Deller wrote:
> On 11/9/23 07:24, Uwe Kleine-König wrote:
> > Hello,
> > 
> > On Wed, Nov 08, 2023 at 10:57:00PM +0100, Helge Deller wrote:
> > > On 11/8/23 22:52, Uwe Kleine-König wrote:
> > > > But info and so info->fix live longer than the probe function, don't
> > > > they?
> > > 
> > > Yes, they do.
> > > But AFAICS info->fix contains a *copy* of the initial atmel_lcdfb_fix struct
> > > (and not a pointer to it). So that should be ok.
> > 
> > If you say so that's good. I grepped a bit around and didn't find a
> > place where a copy is made. But that's probably me and I'll consider the
> > case closed.
> 
> It's not directly obvious, but the copy happens in the line you pointed
> out previously.
> 
> In include/linux/fb.h:
> 
> struct fb_info {
> ...
>         struct fb_var_screeninfo var;   /* Current var */
>         struct fb_fix_screeninfo fix;   /* Current fix */
> 
> so, "fb_info.fix" is a struct, and not a pointer.
> 
> In drivers/video/fbdev/atmel_lcdfb.c:
> static int atmel_lcdfb_probe(struct platform_device *pdev)
> {
> ...
>         info->fix = atmel_lcdfb_fix;  //  (line 1065)
> 
> this becomes effectively a:
> 	memcpy(&info->fix, &atmel_lcdfb_fix, sizeof(struct fb_fix_screeninfo));

Ah right. Thanks for that hint. I didn't spot this and grepped for
memcpy and memdup.

Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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