linux-kernel - Re: [PATCH v2 2/7] x86/boot: Introduce helpers for serial I/O

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Message-ID: <20190328145146.GH9224@smile.fi.intel.com>
Date:   Thu, 28 Mar 2019 16:51:46 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] x86/boot: Introduce helpers for serial I/O

On Thu, Mar 28, 2019 at 03:34:47PM +0100, Borislav Petkov wrote:
> On Thu, Mar 28, 2019 at 04:20:01PM +0200, Andy Shevchenko wrote:
> > By name and by what it's handling (only byte accesses to I/O or MMIO).
> 
> Your series does only byte accesses so you can use byte variant.
> 
> > My point is, that doing branch(es) on each I/O call is not good as simple
> > calling the proper (pre-defined) I/O accessor.
> 
> What branches?

Something like this at the end

if (mmio32)
	...
else if (mmio)
	...
else if (whatever)
	...
else
	...

> You do a branch and *then* you do an IO call.

Yes.

> What does "not good" even mean?

We still export global flag variable, on top of this we need an additional
branch which we can avoid for free.

-- 
With Best Regards,
Andy Shevchenko