i.MX Processors中的主题 Re: C Calling convention Question

C Calling convention Question

davidzhou — Tue, 05 Dec 2017 13:37:26 GMT

Hi,

In kernel/drivers/fbdev/mxsfb.c (line 994): defined mxsfb_ops functions

static struct fb_ops mxsfb_ops = {
   .owner = THIS_MODULE,
   .fb_check_var = mxsfb_check_var,
   .fb_set_par = mxsfb_set_par,
   .fb_setcolreg = mxsfb_setcolreg,
   .fb_ioctl = mxsfb_ioctl,
   .fb_blank = mxsfb_blank,
   .fb_pan_display = mxsfb_pan_display,
   .fb_mmap = mxsfb_mmap,
   .fb_fillrect = cfb_fillrect,
   .fb_copyarea = cfb_copyarea,
   .fb_imageblit = cfb_imageblit,
};

Line 878: defines the function:

static int mxsfb_blank(int blank, struct fb_info *fb_info)
{
struct mxsfb_info *host = to_imxfb_host(fb_info);

host->cur_blank = blank;

...

}

Line 1506: calls the function:

ret = fb_blank(fb_info, FB_BLANK_UNBLANK);

Line 1591: calls the function:

mxsfb_blank(FB_BLANK_POWERDOWN, fb_info);

Why the parameters are passed in with different order?

Thank you,

David Zhou

Re: C Calling convention Question

Carlos_Musich — Tue, 05 Dec 2017 17:13:14 GMT

Hi David,

which kernel are you using?

Re: C Calling convention Question

davidzhou — Tue, 05 Dec 2017 17:23:46 GMT

Hi Carlos,

Thank you for your email regarding my question.

The linux kernel is version 4.1 from DIGI.

The driver passed compilation, and it seems have no problems of running. I just confused myself with the parameters passing sequence.

Thank you,

David Zhou

Re: C Calling convention Question

Carlos_Musich — Tue, 05 Dec 2017 18:23:07 GMT

Hi David,

I find it strange too, but in this case you may contact Digi Embedded because they developed this BSP, not NXP.

Regards,
Carlos

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Re: C Calling convention Question

davidzhou — Tue, 05 Dec 2017 18:49:35 GMT

Hi Calros,

Thank you.

David

Re: C Calling convention Question

davidzhou — Wed, 06 Dec 2017 15:33:34 GMT

Hi Calros

Here is the finding:

In the \linux\fb.h

\linux\fb.h(266): int (*fb_blank)(int blank, struct fb_info *info);

\linux\fb.h(598): extern int fb_blank(struct fb_info *info, int blank);

(That was confusing and not a good practice)

The line (266) has the same signature as

static int mxsfb_blank(int blank, struct fb_info *fb_info);

That explains the structure assignment for the function pointer:

.fb_blank = mxsfb_blank,

And the call of the function in the line 1533:

ret = fb_blank(fb_info, FB_BLANK_UNBLANK);

The function signature is defined as the line 598 (shown above)

The call to the function fb_blank

ret = fb_blank(fb_info, FB_BLANK_UNBLANK);

It is actually defined in the ../fbdev/core/fbmem.c.

Only a little confusion that why not directly call the mxsfb_blank().

David Zhou

Re: C Calling convention Question

zhaoqinsu — Thu, 18 Apr 2019 07:37:56 GMT

Hi David ,

Can you tell me what is the role of three functions ? as below :

    .fb_fillrect = cfb_fillrect,
   .fb_copyarea = cfb_copyarea,
   .fb_imageblit = cfb_imageblit,

Thank you !