[U-Boot] [RFC PATCH v2] ARM: Avoid compiler optimization for usages of readb, writeb and friends.

[John Rigby]

On Mon, Dec 20, 2010 at 5:25 PM, John Rigby <john.rigby at linaro.org> wrote:
> On Mon, Dec 20, 2010 at 10:12 AM, Alexander Holler <holler at ahsoftware.de> wrote:
>
>> There must be more problems. Using gcc 4.5.1, the read*/write*-patch and
>> your hack, my kernel doesn't boot. Using gcc 4.3.5 and the same source to
>> compile u-boot the kernel comes up. Here is the output for the non-working
>> u-boot:
>>
>> ----------------
>> U-Boot 2010.12-rc3-00015-g3ae9687-dirty (Dec 20 2010 - 18:01:41, gcc 4.5.1)
>>
>> OMAP3530-GP ES3.1, CPU-OPP2, L3-165MHz, Max CPU Clock 720 mHz
>> OMAP3 Beagle board + LPDDR/NAND
>> I2C:   ready
>> DRAM:  256 MiB
>> NAND:  256 MiB
>> MMC:   OMAP SD/MMC: 0
>> In:    serial
>> Out:   serial
>> Err:   serial
>> Beagle Rev C4
>> timed out in wait_for_pin: I2C_STAT=0
>> No EEPROM on expansion board
>> Die ID #062a000400000000040365fa16019019
>> Hit any key to stop autoboot:  0
>> reading boot.scr
>>
>> 422 bytes read
>> Running bootscript from mmc ...
>> ## Executing script at 82000000
>> reading uImage
>>
>> 2419940 bytes read
>> Booting from mmc ...
>> ## Booting kernel from Legacy Image at 82000000 ...
>>   Image Name:   Linux-2.6.37-rc5-beagleboard-000
>>   Image Type:   ARM Linux Kernel Image (uncompressed)
>>   Data Size:    2419876 Bytes = 2.3 MiB
>>   Load Address: 80008000
>>   Entry Point:  80008000
>>   Verifying Checksum ... OK
>>   Loading Kernel Image ... OK
>> OK
>> ----------------
>>
>> Nothing else.
>>
>> Regards,
>>
>> Alexander
>>
>
> Yes, you are correct, I see the same here with 4.5.2.  I noticed that
> bd did not have correct values of machine type and boot params:
>
> bd address  = 0x8FF24FE0
> arch_number = 0xFF0084FF
> boot_params = 0xBB2000FE
> DRAM bank   = 0x00000000
> -> start    = 0x80000000
> -> size     = 0x08000000
> DRAM bank   = 0x00000001
> -> start    = 0x88000000
> -> size     = 0x08000000
> baudrate    = 115200 bps
> TLB addr    = 0x8FFF0000
> relocaddr   = 0x8FF85000
> reloc off   = 0x0FF7D000
> irq_sp      = 0x8FF24F68
> sp start    = 0x8FF24F60
> FB base     = 0x00000000
>
> If we then look at board_init in beagle.c the problem is obvious:
>
> 800331ac <board_init>:
> 800331ac:       e92d4008        push    {r3, lr}
> 800331b0:       ebff5a74        bl      80009b88 <gpmc_init>
> 800331b4:       e3a00000        mov     r0, #0
> 800331b8:       e5983000        ldr     r3, [r8]
> 800331bc:       e5983000        ldr     r3, [r8]
> 800331c0:       e8bd8008        pop     {r3, pc}
>

Apparently this is a known issue mentioned in README:

NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
or current versions of GCC may "optimize" the code too much.


With this fix I can boot again:

diff --git a/board/ti/beagle/beagle.c b/board/ti/beagle/beagle.c
index d9b6f01..c066d6e 100644
--- a/board/ti/beagle/beagle.c
+++ b/board/ti/beagle/beagle.c
@@ -51,6 +51,8 @@

 #define BEAGLE_NO_EEPROM               0xffffffff

+DECLARE_GLOBAL_DATA_PTR;
+
 static struct {
        unsigned int device_vendor;
        unsigned char revision;
@@ -66,8 +68,6 @@ static struct {
  */
 int board_init(void)
 {
-       DECLARE_GLOBAL_DATA_PTR;
-
        gpmc_init(); /* in SRAM or SDRAM, finish GPMC */
        /* board id for Linux */
        gd->bd->bi_arch_number = MACH_TYPE_OMAP3_BEAGLE;

Please let me know if you find any other problems.

br,

John