[U-Boot] [PATCH 1/6] usb: ehci: mx6: Add support for i.MX6SL

[Nikolay Dimitrov <picmaster@mail.bg>]

Hi Igor,

On 6/17/2014 9:26 AM, Igor Grinberg wrote:
> That is exactly what we do already (code is on the way) and IMO what 
> we should aim for.
I really didn't knew this in the beginning before seeing your answers, 
this would be definitely easier
to support.

> For me it is just an artificial complication which prevents single binary for
> i.MX6 based boards.
> Don't get me wrong, I think that in your board code you can choose which
> approach you want, whether it will be single or multi binary, but this
> is i.MX6 (and possibly future i.MX*) USB code which can be used on many
> i.MX6 boards.
I definitely like the idea, no argument on this.

> Again, what are we talking about? A couple of bytes? 
I think it will cost 22 additional bytes per check. Here's a rough example:

(Code that just assigns the address to the struct pointer -> 10 bytes)
     p = (mx6_usb_t*)0x55667788;
     8380:       f247 7388       movw    r3, #30600      ; 0x7788
     8384:       f2c5 5366       movt    r3, #21862      ; 0x5566
     8388:       60fb            str     r3, [r7, #12]


(Code that checks in runtime the CPU type -> 32 bytes)
     if (is_imx6q())
     8380:       f7ff ffee       bl      8360 <is_imx6q>
     8384:       4603            mov     r3, r0
     8386:       2b00            cmp     r3, #0
     8388:       d005            beq.n   8396 <main+0x26>
     {
         p = (mx6_usb_t*)0x11223344;
     838a:       f243 3344       movw    r3, #13124      ; 0x3344
     838e:       f2c1 1322       movt    r3, #4386       ; 0x1122
     8392:       60fb            str     r3, [r7, #12]
     8394:       e004            b.n     83a0 <main+0x30>
     }
     else
     {
         p = (mx6_usb_t*)0x55667788;
     8396:       f247 7388       movw    r3, #30600      ; 0x7788
     839a:       f2c5 5366       movt    r3, #21862      ; 0x5566
     839e:       60fb            str     r3, [r7, #12]
     }

If I assume that we have 20 sub-systems in U-Boot, and each needs to 
check the CPU type
in 10 places, this makes 4400 bytes difference, which is roughly the 
size of a moderately
small driver in U-Boot. I need to say that I'm in no way expert in ARM 
assembly, so please
feel free to point out any mistakes in my assumptions.

Please don't get me wrong - I don't want to argue at all. I was just 
wondering about this topic
and decided to check with you guys just to be sure.

Kind regards,
Nikolay