Sam,

On Mon, Jul 8, 2019 at 10:50 AM Sam Ravnborg [off-list ref] wrote:

Hi Dough.

On Mon, Jul 01, 2019 at 09:39:24AM -0700, Doug Anderson wrote:

quoted

Hi,

On Sun, Jun 30, 2019 at 1:22 PM Sam Ravnborg [off-list ref] wrote:

quoted

quoted

@@ -91,6 +92,8 @@ struct panel_simple {
      struct i2c_adapter *ddc;

      struct gpio_desc *enable_gpio;
+
+     struct drm_display_mode override_mode;

I fail to see where this poiter is assigned.

In panel_simple_parse_override_mode().  Specifically:

drm_display_mode_from_videomode(&vm, &panel->override_mode);

The above code-snippet is only called in the panel has specified display
timings using display_timings - it is not called when display_mode is
used.
So override_mode is only assigned in some cases and not all cases.
This needs to be fixed so we do not reference override_mode unless
it is set.

I'm afraid I'm not following you here.

* override_mode is a structure that's directly part of "struct panel_simple".

* The panel is allocated in panel_simple_probe() with devm_kzalloc().

* The "z" in kzalloc means that this memory will be zero-initialized.

From the points above, "override_mode" will always be set to
something.  If we didn't run "drm_display_mode_from_videomode(&vm,
&panel->override_mode);" then we know the entire override_mode
structure will be zero.

While it took a while for me to get used to it, the kernel convention
is to rely on zero-initialization and not to explicitly init things to
zero.  As an example of this being codified in the source, you can see
that "checkpatch.pl" will yell at you for a similar thing: "do not
initialise globals to 0".

quoted

quoted

@@ -152,6 +162,44 @@ static int panel_simple_get_fixed_modes(struct panel_simple *panel)

quoted

              num++;
      }

+     return num;
+}
+
+static int panel_simple_get_non_edid_modes(struct panel_simple *panel)
+{
+     struct drm_connector *connector = panel->base.connector;
+     struct drm_device *drm = panel->base.drm;
+     struct drm_display_mode *mode;
+     bool has_override = panel->override_mode.type;

This looks suspicious.
panel->override_mode.type is an unsigned int that may have a number of
bits set.
So the above code implicitly convert a .type != 0 to a true.
This can be expressed in a much more reader friendly way.

You would suggest that I add a boolean field to a structure to
indicate whether an override mode is present?

A simple  bool has_override = panel->override_mode.type != 0;
would do the trick here.
Then there is no hidden conversion from int to a bool.

I will change this to "panel->override_mode.type != 0" if you're
really sure, but this seems both against the general Linux style
feedback I've received over the years (though there is definitely not
100% consistency) and also against the local convention in this file.
Examples in this file of treating ints as bools without an explicit
"!= 0":

* panel_simple_get_fixed_modes checks "if (panel->desc->bus_format)"
* panel_simple_disable checks "if (p->desc->delay.disable)"
* panel_simple_unprepare checks "if (p->desc->delay.unprepare)"
* panel_simple_prepare checks "if (delay)"
* panel_simple_enable checks "if (p->desc->delay.enable)"

...and, although slightly different, pointers in this file are checked
for NULL vs. non-NULL without an explicit "== NULL".

Of course just because all the other examples in the file do it one
way doesn't mean that new code has to do it another way, but I wanted
to be really sure you wanted me to go against the existing convention
before changing this.

But as override_mode can be NULL something more needs to be done.

I'm afraid I don't understand how override_mode can be NULL since it's
not a pointer.  Can you clarify?


-Doug
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