Dear Ben,
in message 4A9069E9.2030000@gmail.com you wrote:
Tested on mx31ads: works like a charm.
Great news! Thanks!
Wait... we've not reached the goal yet, I'm afraid...
Will try to debug the trab issues later tonight (if I manage to find a matching JTAG connector for this board ).
This turns out to be a nasty one.
The good news is: the hang on trab is not caused by your patch.
Fact is that it is instead caused by using a somewhat recent (gcc-4.2.2 based) tool chain. This compiler does some ugly things when attempting to access 32 bit wide registers which cause one of the trab-specific drivers to hang in the initialization. If I use an older tool chain (say, gcc-4.0.0 based), your patch works like a charm, too.
The bad news ist: I don't know how to fix this.
In the first attempt I noticed that the (old) trab code does not use any I/O accessors at all. My guesses that a "volatile" might be missing didn't help.
So I changed the code in question to use readl() / writel() - and this did not help either.
Then I noticed that readl() / writel() on ARM are mapped to __arch_getl() / __arch_putl() which in turn are just plain stupid volatile pointer accesses.
So I replaced these #defines by the following code:
static inline uint32_t __arch_getl (uint32_t V_ATTRIB * const addr) { uint32_t val; val = *addr; return val; }
static inline void __arch_putl (uint32_t val, uint32_t V_ATTRIB * const addr) { *addr = val; }
With this code, I see the following behaviour:
1) If I use "#define V_ATTRIB volatile" which I think is needed and technically correct, the trab-specific driver code starts working again; however, the CS8900 Ethernet driver does not work. It gives:
TRAB # run load Using CS8900-0 device TFTP from server 192.168.1.1; our IP address is 192.168.20.2 Filename '/tftpboot/trab/u-boot.bin'. Load address: 0xc100000 Loading: T T T T T T T T T T Retry count exceeded; starting again Using CS8900-0 device TFTP from server 192.168.1.1; our IP address is 192.168.20.2 Filename '/tftpboot/trab/u-boot.bin'. Load address: 0xc100000 Loading: T T T T T T T T T T Retry count exceeded; starting again Using CS8900-0 device TFTP from server 192.168.1.1; our IP address is 192.168.20.2 Filename '/tftpboot/trab/u-boot.bin'. Load address: 0xc100000 Loading: T T T T T T T T T T Retry count exceeded; starting again ...
All this in quick sequence, without the usual longish delays / timeouts.
2) If I use "#define V_ATTRIB" instead (i. e. if I do _not_ use "volatile"), then the trab driver code hangs again, but the CS8900 Ethernet driver works fine.
It seems the "volatile" causes the compiler to generate different code - with the volatile it seems that 4 x 8 bit reads are performed instead of 1 x 32 bit read. Unfortunaltely I wasn't able to reduce this to a trival test case yet.
Is there anybody out there with good C compiler / assembler knowhow on ARM - and with an idea how to fix this issue?
Best regards,
Wolfgang Denk