> -----Original Message-----
> From: Laszlo Ersek [mailto:ler...@redhat.com]
> Sent: Friday, February 23, 2018 4:52 PM
> To: Pankaj Bansal <pankaj.ban...@nxp.com>; Udit Kumar
> <udit.ku...@nxp.com>; Leif Lindholm <leif.lindh...@linaro.org>
> Cc: michael.d.kin...@intel.com; edk2-devel@lists.01.org;
> ard.biesheu...@linaro.org; Meenakshi Aggarwal
> <meenakshi.aggar...@nxp.com>
> Subject: Re: [edk2] [PATCH edk2-platforms 01/39] Silicon/NXP: Add support
> for Big Endian Mmio APIs
> 
> On 02/23/18 12:04, Pankaj Bansal wrote:
> 
> > However Laszlo, with the method you suggest (using STATIC CONST
> > UINT16 mOne), would it not add delay in each Mmio Operation ?
> >
> > I am concerned about boot delay using this approach.
> The condition can be evaluated at compile time, so I expect optimizing
> compilers to eliminate the dead branch.
> 
> Assuming the condition cannot be eliminated at build time, what is your
> concern: the single byte access, or the branch instruction?
> 
> I don't think the single byte access matters. (If you tried to replace that 
> with a
> HOB or PCD lookup, it could only be worse.)
> 
> I also doubt the branch should be a concern. You could replace the "if"
> (or the ternary operator "?:") with function pointers that you set e.g.
> in a constructor function. But I think an "if" with an invariable
> (constant) controlling expression is at least as friendly towards branch
> predictors as a function pointer variable (through which you might be
> *forced* to make a real function call).
> 
> Personally I wouldn't worry.
> 

I think you are right about smart compiler eliminating the branches at build 
time.
I just pointed this out because we call Mmio/BeMmio APIs when accessing Nor 
flash for variable read/write.
As these are called so many time during boot, I did not want any delay to be 
added to these APIs than necessary.
Now that you have pointed it out, I don't think any significant delay will be 
added to these APIs.

> 
> Anyway: please do not mistake my willingness / preference to go into such
> detail for having high stakes at this. If you go an entirely different route, 
> I'm
> OK with that too. I felt I was asked for my opinion and I tried to express it 
> in
> detail, that's all.

Any comments/suggestions/opinions are always appreciated from you or from any 
edk2 mailing list member.

> 
> Thanks
> Laszlo
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