[coreboot] patch: fix USB ports on DBE62, and other cs5536-based platforms

[ron minnich]

On Wed, Jun 4, 2008 at 9:46 AM, Marc Jones <Marc.Jones at amd.com> wrote:
> ron minnich wrote:
>> This change adds some debug prints, and a comment warning to dts on cs5536.
>>
>> Most importantly it fixes a simple programming error which made it so most of
>> the sets on the USB were not doing anything. The bug is also in V2.
>>
>
>
>> /* the /sizeof(u32) is to convert byte offsets into u32 offsets */
>> #define HCCPARAMS             (0x08/sizeof(u32))
>
>
>
> I don't understand this change. This is standard MMIO. The memory mapped
> registers are defined 0h, 04h, 08h, 0Ah...
>
> You could
> *(bar + 08h) |= 1 << 9;
> or
> *(bar + 09h) |= 1 << 1;
>


This is an old C gotcha. Offsets are scaled by the pointer size. bar
is a u32 *. So you see this:
*(bar + HCCPARAMS)

And it's easy to think that it is this:
*(bar + 0xc)

but actually, because bar is a u32 *, it will actually dereference this:
*(bar + 0xc*4) i.e. the sizeof a u32 ...

It has to work this way, because when you do bar++, it increments bar
by 4, not 1.

This is one of the reasons why, for mmio, we ought to be using structs.

thanks

ron