Re: [PATCH 02/22] fb: atmel_lcdfb: Stop using platform_driver_probe()

[Helge Deller <deller@gmx.de>]

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));

so, the compiler copies the "__initconst" data over to the info->fix struct.

Helge