[U-Boot] [PATCH 0/5] Create an API for safely accessing BMP header fields

[Albert ARIBAUD]

Hi Tom,

On Tue, 5 Feb 2013 09:58:52 -0500, Tom Rini <trini at ti.com> wrote:

> On Mon, Feb 04, 2013 at 03:19:56PM +0100, Albert ARIBAUD wrote:
> > Hi Nikita,
> > 
> > On Mon, 04 Feb 2013 14:37:06 +0200, Nikita Kiryanov
> > <nikita at compulab.co.il> wrote:
> > 
> > > Hi Albert,
> > > 
> > > On 02/04/2013 01:57 PM, Albert ARIBAUD wrote:
> > > >
> > > > IIRC, you has submitted a fix so that BMP loads would result in
> > > > correctly aligned fields and thus no need for accessors. Why this
> > > > change of mind?
> > >  >
> > > 
> > > I did mention that I consider that fix as temporary. I believe this fix
> > > is better because it addresses the issue everywhere and does so in a
> > > more maintainable way (does not require the address fix to be duplicated
> > > everywhere there is a problem).
> > 
> > I actually like the new fix less, as it adds an API where there is no
> > need of one -- it's not like the implementation of BMP is at risk of
> > changing. What is the problem in fixing the load address at load time
> > and then passing this fixed address around?
> 
> OK, so I'm wondering.  Isn't this an example of where our idea that
> unaligned accesses are a software problem to fix, rather than an area to
> let the hardware fixup for us, when able, is wrong?
> 
> In other words, a real life example of why we should go with
> -munaligned-access being set for v7, set the HW bit and let things go?

I feel this is addressed to me. :)

And no, I don't think the BMP issue should be solved by relaxing HW
constraints. BMP is not a HW-enforced or protocol format.

Anyway, as I said, even if we really could not avoid misaligned
fields (and we know at least two ways we could), then the solution would
not be to flip a general HW switch controlling all accesses, since
only the BMP accesses are a problem! We could just make sure we access
the poorly aligned fields through dedicated unaligned accessors, e.g.
readl_u(&field) / writel_u(&field).

Amicalement,
-- 
Albert.