[U-Boot] [PATCH] dm: video: fix abuse of enum

[Lothar Waßmann]

Hi,

On Wed, 5 Jul 2017 22:49:28 -0600 Simon Glass wrote:
> Hi Lothar,
> 
> On 23 June 2017 at 00:30, Lothar Waßmann <LW at karo-electronics.de> wrote:
> > Hi,
> >
> > On Wed, 21 Jun 2017 09:59:05 +0200 Lothar Waßmann wrote:
> >> Hi,
> >>
> >> On Tue, 20 Jun 2017 12:26:29 -0600 Simon Glass wrote:
> >> > Hi Lothar,
> >> >
> >> > On 20 June 2017 at 04:25, Lothar Waßmann <LW at karo-electronics.de> wrote:
> >> > > LCD_MAX_WIDTH, LCD_MAX_HEIGHT and LCD_MAX_LSBPP are not alternative
> >> > > values for one specific variable, but unrelated entities with distinct
> >> > > purposes. There is no use defining them as values of an 'enum'.
> >> >
> >> > Can you explain why #define is better? I prefer enum since they are a
> >> > compiler construct instead of preprocessor (thus no need for brackets,
> >> > no strange conversion things) and the debugger knows about them.
> >> >
> >> An enum defines alternative values for one specific entity (e.g.
> >> clauses for a switch construct), but not a collection of arbitrary data
> >> items.
> >>
> >> > > The 'enum' construct would fail miserably for an LCD controller that
> >> > > has a square max. frame size (e.g. 4096x4096).
> >> >
> >> > What does this mean? I don't understand sorry.
> >> >
> >> Try your enum with MAX_LCD_WITDH == MAC_LCD_HEIGHT.
> 
> Can you please be explicit as to what the problem is? Sorry but I
> don't understand what you are driving at. Do you have a test program
> which shows the problem?
> 
You cannot have two different enum items with the same value!
Thus:
enum {
	MAX_LCD_WIDTH = 4096,
	MAX_LCD_HEIGHT = 4096,
};
won't compile.


The purpose of an enum is to provide a collection of possible values
that can be taken by a single variable. E.g. enumerate the states of a
state machine, video modes, CPU types...
It's not meant to group together otherwise unsolicited values.


Lothar Waßmann