śr., 20 lis 2019 o 20:26 Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> napisał(a): > > On Wed, Oct 23, 2019 at 11:47:04AM +0200, Mateusz Holenko wrote: > > +#ifdef __LITTLE_ENDIAN > > +# define LITEX_READ_REG(addr) ioread32(addr) > > +# define LITEX_READ_REG_OFF(addr, off) ioread32(addr + off) > > +# define LITEX_WRITE_REG(val, addr) iowrite32(val, addr) > > +# define LITEX_WRITE_REG_OFF(val, addr, off) iowrite32(val, addr + off) > > +#else > > +# define LITEX_READ_REG(addr) ioread32be(addr) > > +# define LITEX_READ_REG_OFF(addr, off) ioread32be(addr + off) > > +# define LITEX_WRITE_REG(val, addr) iowrite32be(val, addr) > > +# define LITEX_WRITE_REG_OFF(val, addr, off) iowrite32be(val, addr + off) > > +#endif > > I just noticed this. > > Ick, this is not good. You will run into problems in the future with > this, I can guarantee it. What about systems where the CPU is one > endian and the hardware in the other? It will happen trust us. As mentioned in the previous comment, LiteX CSRs are guaranteed to be always little-endian - this includes configurations with both big-endian and little-endian CPUs. The aim of including the ifdef section was exactly to target situation where endianness is different for CPU and devices. As such this approach *should* work. > Make these real functions (inline is nice) and pass in the pointer to > the device so you can test for it and call the correct function based on > the cpu/hardware type. > > And what about bitfields? What endian are they for your > system/hardware? > > Almost no kernel code should EVER be testing __LITTLE_ENDIAN, don't add > to it as it is not a good idea. If I understand correctly, you suggest to replace compile-time ifdefing with probing the endianness in the runtime (by reading some register that should return a known value, say 1, and testing how bits are arranged). This is a good idea, as it protects against breaking an always-little-endian property of LiteX CSRs in the future. I'll include this in the next version of the patchset. > thanks, > > greg k-h Thanks for your comments! -- Mateusz Holenko Antmicro Ltd | www.antmicro.com Roosevelta 22, 60-829 Poznan, Poland
