Hi Nikolay,
On 06/17/14 20:49, Nikolay Dimitrov wrote:
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.
This looks like a very rough estimation. It also can be improved by various ways.
Anyway, I think that even 4K addition is an acceptable compromise for a single binary.
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.
No problem.