fbdev: omapfb: panel-sony-acx565akm: Simplify show_cabc_available_modes()

Use sysfs_emit_at() instead of snprintf() + custom logic.
Using sysfs_emit_at() is much more simple.

Also, sysfs_emit() is already used in this function, so using
sysfs_emit_at() is more consistent.

Also simplify the logic:
  - always add a space after an entry
  - change the last space into a '\n'

Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
can not be reached.
So better keep everything simple (and correct).

Signed-off-by: Christophe JAILLET <redacted>
---
 .../omap2/omapfb/displays/panel-sony-acx565akm.c  | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
index 71d2e015960c..fc975615d5c9 100644
--- a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
+++ b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c

@@ -466,19 +466,20 @@ static ssize_t show_cabc_available_modes(struct device *dev,
 		char *buf)
 {
 	struct panel_drv_data *ddata = dev_get_drvdata(dev);
-	int len;
+	int len = 0;
 	int i;
 
 	if (!ddata->has_cabc)
 		return sysfs_emit(buf, "%s\n", cabc_modes[0]);
 
-	for (i = 0, len = 0;
-	     len < PAGE_SIZE && i < ARRAY_SIZE(cabc_modes); i++)
-		len += snprintf(&buf[len], PAGE_SIZE - len, "%s%s%s",
-			i ? " " : "", cabc_modes[i],
-			i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");
+	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)
+		len += sysfs_emit_at(buf, len, "%s ", cabc_modes[i]);
+
+	/* Remove the trailing space */
+	if (len)
+		buf[len - 1] = '\n';
 
-	return len < PAGE_SIZE ? len : PAGE_SIZE - 1;
+	return len;
 }
 
 static DEVICE_ATTR(cabc_mode, S_IRUGO | S_IWUSR,

-- 
2.46.0

Hi Christophe,

On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:

Use sysfs_emit_at() instead of snprintf() + custom logic.
Using sysfs_emit_at() is much more simple.

Also, sysfs_emit() is already used in this function, so using
sysfs_emit_at() is more consistent.

Also simplify the logic:
  - always add a space after an entry
  - change the last space into a '\n'

Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
can not be reached.
So better keep everything simple (and correct).

Signed-off-by: Christophe JAILLET <redacted>

neat!

Reviewed-by: Andi Shyti <redacted>

Andi

On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:

5 more quoted lines

I'm uncomfortable with this line.  It assumes we don't overflow PAGE_SIZE where
the original code was careful about checking.  Probably easiest to do what the
original code did and say:

	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)
		len += sysfs_emit_at(buf, len, "%s%s", cabc_modes[i],
				     i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");

regards,
dan carpenter

On Fri, Aug 09, 2024 at 05:42:32PM +0300, Dan Carpenter wrote:

On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:

quoted

Use sysfs_emit_at() instead of snprintf() + custom logic.
Using sysfs_emit_at() is much more simple.

Also, sysfs_emit() is already used in this function, so using
sysfs_emit_at() is more consistent.

Also simplify the logic:
  - always add a space after an entry
  - change the last space into a '\n'

Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
can not be reached.
So better keep everything simple (and correct).

Signed-off-by: Christophe JAILLET <redacted>
---
 .../omap2/omapfb/displays/panel-sony-acx565akm.c  | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
index 71d2e015960c..fc975615d5c9 100644
--- a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
+++ b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c

@@ -466,19 +466,20 @@ static ssize_t show_cabc_available_modes(struct device *dev,
 		char *buf)
 {
 	struct panel_drv_data *ddata = dev_get_drvdata(dev);
-	int len;
+	int len = 0;
 	int i;
 
 	if (!ddata->has_cabc)
 		return sysfs_emit(buf, "%s\n", cabc_modes[0]);
 
-	for (i = 0, len = 0;
-	     len < PAGE_SIZE && i < ARRAY_SIZE(cabc_modes); i++)
-		len += snprintf(&buf[len], PAGE_SIZE - len, "%s%s%s",
-			i ? " " : "", cabc_modes[i],
-			i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");

14 more quoted lines

Or you could change it to:

	if (len)
		sysfs_emit_at(buf, len - 1, "\n");

But that feels weird.

regards,
dan carpenter

Le 09/08/2024 à 16:42, Dan Carpenter a écrit :

On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:

quoted

Use sysfs_emit_at() instead of snprintf() + custom logic.
Using sysfs_emit_at() is much more simple.

Also, sysfs_emit() is already used in this function, so using
sysfs_emit_at() is more consistent.

Also simplify the logic:
   - always add a space after an entry
   - change the last space into a '\n'

Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
can not be reached.
So better keep everything simple (and correct).

Signed-off-by: Christophe JAILLET <redacted>
---
  .../omap2/omapfb/displays/panel-sony-acx565akm.c  | 15 ++++++++-------
  1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
index 71d2e015960c..fc975615d5c9 100644
--- a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
+++ b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c

@@ -466,19 +466,20 @@ static ssize_t show_cabc_available_modes(struct device *dev,
  		char *buf)
  {
  	struct panel_drv_data *ddata = dev_get_drvdata(dev);
-	int len;
+	int len = 0;
  	int i;
  
  	if (!ddata->has_cabc)
  		return sysfs_emit(buf, "%s\n", cabc_modes[0]);
  
-	for (i = 0, len = 0;
-	     len < PAGE_SIZE && i < ARRAY_SIZE(cabc_modes); i++)
-		len += snprintf(&buf[len], PAGE_SIZE - len, "%s%s%s",
-			i ? " " : "", cabc_modes[i],
-			i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");

11 more quoted lines

Hi Dan,

I don't follow you. AFAIK, it does not assume anything.

Thanks to sysfs_emit_at(), len can only be in [0..PAGE_SIZE-1] because the trailing \0 is not counted.

So, as len != 0, len-1 is in [0..PAGE_SIZE-2].

How do you think an overflow could happen?


Also, all this code does is buildind:
	"off, ui, still-image, moving-image\n"

So in any case, an overflow is impossible, and really unlikely in the future as well.


From my PoV, my proposed patch is both much more readable and still correct in all cases.

CJ

	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)
		len += sysfs_emit_at(buf, len, "%s%s", cabc_modes[i],
				     i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");

regards,
dan carpenter

On Fri, Aug 09, 2024 at 05:09:28PM +0200, Christophe JAILLET wrote:

Le 09/08/2024 à 16:42, Dan Carpenter a écrit :

quoted

On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:

quoted

Use sysfs_emit_at() instead of snprintf() + custom logic.
Using sysfs_emit_at() is much more simple.

Also, sysfs_emit() is already used in this function, so using
sysfs_emit_at() is more consistent.

Also simplify the logic:
   - always add a space after an entry
   - change the last space into a '\n'

Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
can not be reached.
So better keep everything simple (and correct).

Signed-off-by: Christophe JAILLET <redacted>
---
  .../omap2/omapfb/displays/panel-sony-acx565akm.c  | 15 ++++++++-------
  1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
index 71d2e015960c..fc975615d5c9 100644
--- a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
+++ b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c

@@ -466,19 +466,20 @@ static ssize_t show_cabc_available_modes(struct device *dev,
  		char *buf)
  {
  	struct panel_drv_data *ddata = dev_get_drvdata(dev);
-	int len;
+	int len = 0;
  	int i;
  	if (!ddata->has_cabc)
  		return sysfs_emit(buf, "%s\n", cabc_modes[0]);
-	for (i = 0, len = 0;
-	     len < PAGE_SIZE && i < ARRAY_SIZE(cabc_modes); i++)
-		len += snprintf(&buf[len], PAGE_SIZE - len, "%s%s%s",
-			i ? " " : "", cabc_modes[i],
-			i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");
+	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)

18 more quoted lines

Ah, you're right.  Sorry for the noise.

regards,
dan carpenter

On 8/8/24 11:46, Christophe JAILLET wrote:

Use sysfs_emit_at() instead of snprintf() + custom logic.
Using sysfs_emit_at() is much more simple.

Also, sysfs_emit() is already used in this function, so using
sysfs_emit_at() is more consistent.

Also simplify the logic:
   - always add a space after an entry
   - change the last space into a '\n'

Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
can not be reached.
So better keep everything simple (and correct).

Signed-off-by: Christophe JAILLET <redacted>

applied.

Thanks!
Helge