Hi, On Mon, Oct 16, 2017 at 4:00 PM, Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > Hi, > > I've applied all the other patches. > > On Sat, Oct 14, 2017 at 12:02:50PM +0800, Chen-Yu Tsai wrote: >> The display backend, as well as other peripherals that have a DRAM >> clock gate and access DRAM directly, bypassing the system bus, >> address the DRAM starting from 0x0, while physical addresses the >> system uses starts from 0x40000000 (or 0x20000000 in A80's case). >> >> Correct the address configured into the backend layer registers >> by PHYS_OFFSET to account for this. > > However, I'm a bit confused at this. > > The driver has been working so far, which it wouldn't have been able > to if the address was wrong. How was this problem noticed, and how can > that fix not be an issue in itself? This problem was witnessed on the Cubietruck, which has 2GB of RAM. I believe devices with less RAM function normally due to the DRAM address wrapping around. CMA seems to always allocate its buffer at a very high address, close to the end of DRAM. On a 1GB RAM device, the physical address would be something like 0x78000000. The DRAM address 0x78000000 would access the same DRAM region as 0x38000000 on a system, as the DRAM address would only span 0x0 ~ 0x3fffffff. The bit 0x40000000 is non-functional in this case. However on the Cubietruck, the DRAM is 2GB. The physical address is 0x40000000 ~ 0xbfffffff. The buffer would be something like 0xb8000000. But the DRAM address span 0x0 ~ 0x7fffffff, meaning the buffer address wraps around to 0x38000000, which is wrong. The correct DRAM address for it should be 0x78000000. ChenYu > > Thanks! > Maxime > > -- > Maxime Ripard, Free Electrons > Embedded Linux and Kernel engineering > http://free-electrons.com > > -- > You received this message because you are subscribed to the Google Groups "linux-sunxi" group. > To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscribe@xxxxxxxxxxxxxxxx. > For more options, visit https://groups.google.com/d/optout. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
