Hi Ard.
Response inline below
> -----Original Message-----
> From: Ard Biesheuvel [mailto:[email protected]]
> Sent: 12 October 2017 20:47
> To: Evan Lloyd <[email protected]>
> Cc: [email protected]; "[email protected]"@arm.com;
> "[email protected]"@arm.com;
> "[email protected]"@arm.com; "[email protected]"@arm.com
> Subject: Re: [PATCH 03/19] ArmPlatformPkg: PL111 and HDLCD: add const
> qualifier
>
> On 26 September 2017 at 21:15, <[email protected]> wrote:
> > From: Girish Pathak <[email protected]>
> >
> > This change adds some STATIC and CONST qualifiers (mainly to arguments
> > of functions) in PL111 and HdLcd modules.
> >
> > It doesn't add or modify any functionality.
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Girish Pathak <[email protected]>
> > Signed-off-by: Evan Lloyd <[email protected]>
> > ---
> >
> ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdAr
> mVExpress.c | 34 ++++++++++----------
> >
> ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL11
> 1LcdArmVExpress.c | 34 ++++++++++----------
> > ArmPlatformPkg/Drivers/LcdGraphicsOutputDxe/HdLcd.c
> | 4 +--
> > ArmPlatformPkg/Drivers/LcdGraphicsOutputDxe/PL111Lcd.c
> | 4 +--
> > 4 files changed, 38 insertions(+), 38 deletions(-)
> >
> > diff --git
> >
> a/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcd
> ArmVE
> > xpress.c
> >
> b/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcd
> ArmVE
> > xpress.c index
> >
> cfe3259d3c737de240350e8c3eab867b80c40948..b9859a56988f7e5be0ad
> baa49048
> > a683fe586bfe 100644
> > ---
> >
> a/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcd
> ArmVE
> > xpress.c
> > +++
> b/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcd
> A
> > +++ rmVExpress.c
> > @@ -46,7 +46,7 @@ typedef struct {
> >
> > /** The display modes supported by the platform.
> > **/
> > -LCD_RESOLUTION mResolutions[] = {
> > +STATIC CONST LCD_RESOLUTION mResolutions[] = {
> > { // Mode 0 : VGA : 640 x 480 x 24 bpp
> > VGA, VGA_H_RES_PIXELS, VGA_V_RES_PIXELS,
> LCD_BITS_PER_PIXEL_24,
> > VGA_OSC_FREQUENCY,
> > @@ -144,8 +144,8 @@ LcdPlatformInitializeDisplay ( **/ EFI_STATUS
> > LcdPlatformGetVram (
> > - OUT EFI_PHYSICAL_ADDRESS* VramBaseAddress,
> > - OUT UINTN* VramSize
> > + OUT EFI_PHYSICAL_ADDRESS * CONST VramBaseAddress,
> > + OUT UINTN * CONST VramSize
>
> What is the point of this CONST (and all the other occurrences in this patch)
>
> In all cases [AFAICT] the CONST applies to the argument itself, not to the
> object it points to, which means the variable is CONST in the scope of the
> function, but can still be dereferenced to assign the OUT value.
>
> This means your change is technically correct, but it is extremely
> unidiomatic for EDK2, so an explanation why this driver needs this would be
> highly appreciated.
>
[[Evan Lloyd]] The style is explicitly sanctioned by the Edk2 CCS ยง 5.6.2.4.2
" Constant pointer to variable: UINTN * CONST ConstPointer;
ConstPointer is a constant pointer to a variable UINTN."
The real benefit is that it clearly identifies the pointer as not changed in
the function.
In this specific instance that also makes it obvious that the OUT parameters
are not array bases, just pointers to individual values.
On a broader note - why would you ever not have a const where something is not
modified?
As another view, the "unidiomatic for EDK2" argument implies you have a very
high opinion of the existing ArmPlatformPkg code quality.
The "we have always done it that way" argument does not encourage quality
improvements.
Regards,
Evan
> > )
...
> > --
> > Guid("CE165669-3EF3-493F-B85D-6190EE5B9759")
> >
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