Re: [PATCH] Platform/ARM/VExpress: refine the check for DVI support

[Leif Lindholm <leif.lindholm@linaro.org>]

On Fri, Jan 26, 2018 at 10:34:59PM +0530, Thomas Abraham wrote:
> The base models could have different values for the revision ID field
> in the System ID register. Base models do not have support for DVI
> and so the revision ID field should also be masked out when checking
> for the presence of DVI support.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
> ---
>  .../VExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c    | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Platform/ARM/VExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c b/Platform/ARM/VExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c
> index 3f3ceb3..89ba130 100644
> --- a/Platform/ARM/VExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c
> +++ b/Platform/ARM/VExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c
> @@ -264,7 +264,7 @@ LcdPlatformSetMode (
>    SysId = MmioRead32 (ARM_VE_SYS_ID_REG);
>    if (SysId != ARM_RTSM_SYS_ID) {
>      // Take out the FVP GIC variant to reduce the permutations.
> -    SysId &= ~ARM_FVP_SYS_ID_VARIANT_MASK;
> +    SysId &= ~(ARM_FVP_SYS_ID_VARIANT_MASK | ARM_FVP_SYS_ID_REV_MASK);
>      if (SysId != ARM_FVP_BASE_BOARD_SYS_ID) {
>        // Set the DVI into the new mode
>        Status = ArmPlatformSysConfigSet (SYS_CFG_DVIMODE, mResolutions[ModeNumber].Mode);

I think this change makes sense (and should arguably have been there
from the start). But I also think it highlights that the surrounding
comments are incorrect, and get increasingly confusing with this
modification.

I would suggest that
  // On the FVP models the GIC variant in encoded in bits [15:12].
is replaced by
  // On the FVP models, the build variant is encoded in bits [15:12].

and that
  // Take out the FVP GIC variant to reduce the permutations.
is replaced by
  // Ignore build variant and revision.

If you're happy with that, I can fold these changes to the surrounding
comments in and commit.

/
    Leif