I am using PPC440x5 Cpu core. How to check the chip-select flash is using? Earlier I have run the same code for M29W128GH and it works fine. But with S29GL512 it is not working. Now the difference is only in size and write/read timings. So I believe it should work in smooth manner.
Hmm.. If you're supposed to boot from this device, then I assume the flash is connected to CS0.For slow devices, the memory controller is usually setup to use the GPCM. Check your options and base registers (OR0 and BR0). Everything related to timing (for GPCM controlled devices) is done in these two registers.
If you have a BDI JTAG, you can set these registers using that and try to perform flash operations from here. Again, if you can, try to access the flash using the JTAG before experimenting with U-Boot.
You mention different size.. is the port size different too?
In order to help you, I think the community needs more info about your system. Stefan asked for logs, etc.
Regards, Frank