Problem reading and programming memory location...

[neorf3k]

we have tried to read and program an 8bit register with 32bit address. we have mapped it with: ioremap, kmalloc etc… and then using: outb, iowrite8 etc.. but when we write to it, the value doesn’t change… with other memory location is ok.
That is an 8 bit register, located at 0x10020000 in a mpc5200b architecture. we are using kernel 2.6.33. 
what could be?
Thank you

Lorenzo