2020-07-23 17:03:06

by Colin King

Subject: [PATCH] video: fbdev: fix setting of pixclock because a pass-by-value error

From: Colin Ian King <[email protected]>

The pixclock is being set locally because it is being passed as a
pass-by-value argument rather than pass-by-reference, so the computed
pixclock is never being set in var->pixclock. Fix this by passing
by reference.

[This dates back to 2002, I found the offending commit from the git
history git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git ]

Addresses-Coverity: ("Unused value")
Fixes: 115f4504a64a ("Removed currcon and other console related code. Very little is now left.")
Signed-off-by: Colin Ian King <[email protected]>
---
drivers/video/fbdev/vga16fb.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c
index a20eeb8308ff..52f273af6cae 100644
--- a/drivers/video/fbdev/vga16fb.c
+++ b/drivers/video/fbdev/vga16fb.c
@@ -243,7 +243,7 @@ static void vga16fb_update_fix(struct fb_info *info)
}

static void vga16fb_clock_chip(struct vga16fb_par *par,
- unsigned int pixclock,
+ unsigned int *pixclock,
const struct fb_info *info,
int mul, int div)
{
@@ -259,14 +259,14 @@ static void vga16fb_clock_chip(struct vga16fb_par *par,
{ 0 /* bad */, 0x00, 0x00}};
int err;

- pixclock = (pixclock * mul) / div;
+ *pixclock = (*pixclock * mul) / div;
best = vgaclocks;
- err = pixclock - best->pixclock;
+ err = *pixclock - best->pixclock;
if (err < 0) err = -err;
for (ptr = vgaclocks + 1; ptr->pixclock; ptr++) {
int tmp;

- tmp = pixclock - ptr->pixclock;
+ tmp = *pixclock - ptr->pixclock;
if (tmp < 0) tmp = -tmp;
if (tmp < err) {
err = tmp;
@@ -275,7 +275,7 @@ static void vga16fb_clock_chip(struct vga16fb_par *par,
}
par->misc |= best->misc;
par->clkdiv = best->seq_clock_mode;
- pixclock = (best->pixclock * div) / mul;
+ *pixclock = (best->pixclock * div) / mul;
}

#define FAIL(X) return -EINVAL
@@ -497,10 +497,10 @@ static int vga16fb_check_var(struct fb_var_screeninfo *var,

if (mode & MODE_8BPP)
/* pixel clock == vga clock / 2 */
- vga16fb_clock_chip(par, var->pixclock, info, 1, 2);
+ vga16fb_clock_chip(par, &var->pixclock, info, 1, 2);
else
/* pixel clock == vga clock */
- vga16fb_clock_chip(par, var->pixclock, info, 1, 1);
+ vga16fb_clock_chip(par, &var->pixclock, info, 1, 1);

var->red.offset = var->green.offset = var->blue.offset =
var->transp.offset = 0;
--
2.27.0

2020-09-08 13:11:35

by Bartlomiej Zolnierkiewicz

Subject: Re: [PATCH] video: fbdev: fix setting of pixclock because a pass-by-value error

On 7/23/20 7:02 PM, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> The pixclock is being set locally because it is being passed as a
> pass-by-value argument rather than pass-by-reference, so the computed
> pixclock is never being set in var->pixclock. Fix this by passing
> by reference.
>
> [This dates back to 2002, I found the offending commit from the git
> history git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git ]
>
> Addresses-Coverity: ("Unused value")
> Fixes: 115f4504a64a ("Removed currcon and other console related code. Very little is now left.")
> Signed-off-by: Colin Ian King <[email protected]>

Applied to drm-misc-next tree, thanks and sorry for the delay.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> ---
> drivers/video/fbdev/vga16fb.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c
> index a20eeb8308ff..52f273af6cae 100644
> --- a/drivers/video/fbdev/vga16fb.c
> +++ b/drivers/video/fbdev/vga16fb.c
> @@ -243,7 +243,7 @@ static void vga16fb_update_fix(struct fb_info *info)
> }
>
> static void vga16fb_clock_chip(struct vga16fb_par *par,
> - unsigned int pixclock,
> + unsigned int *pixclock,
> const struct fb_info *info,
> int mul, int div)
> {
> @@ -259,14 +259,14 @@ static void vga16fb_clock_chip(struct vga16fb_par *par,
> { 0 /* bad */, 0x00, 0x00}};
> int err;
>
> - pixclock = (pixclock * mul) / div;
> + *pixclock = (*pixclock * mul) / div;
> best = vgaclocks;
> - err = pixclock - best->pixclock;
> + err = *pixclock - best->pixclock;
> if (err < 0) err = -err;
> for (ptr = vgaclocks + 1; ptr->pixclock; ptr++) {
> int tmp;
>
> - tmp = pixclock - ptr->pixclock;
> + tmp = *pixclock - ptr->pixclock;
> if (tmp < 0) tmp = -tmp;
> if (tmp < err) {
> err = tmp;
> @@ -275,7 +275,7 @@ static void vga16fb_clock_chip(struct vga16fb_par *par,
> }
> par->misc |= best->misc;
> par->clkdiv = best->seq_clock_mode;
> - pixclock = (best->pixclock * div) / mul;
> + *pixclock = (best->pixclock * div) / mul;
> }
>
> #define FAIL(X) return -EINVAL
> @@ -497,10 +497,10 @@ static int vga16fb_check_var(struct fb_var_screeninfo *var,
>
> if (mode & MODE_8BPP)
> /* pixel clock == vga clock / 2 */
> - vga16fb_clock_chip(par, var->pixclock, info, 1, 2);
> + vga16fb_clock_chip(par, &var->pixclock, info, 1, 2);
> else
> /* pixel clock == vga clock */
> - vga16fb_clock_chip(par, var->pixclock, info, 1, 1);
> + vga16fb_clock_chip(par, &var->pixclock, info, 1, 1);
>
> var->red.offset = var->green.offset = var->blue.offset =
> var->transp.offset = 0;
>