On Tue, 7 Jul 2020 at 10:39, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Ard, > > On Tue, Jul 7, 2020 at 8:50 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > On Mon, 6 Jul 2020 at 18:02, Geert Uytterhoeven <geert+renesas@xxxxxxxxx> wrote: > > > Currently, the start address of physical memory is obtained by masking > > > the program counter with a fixed mask of 0xf8000000. This mask value > > > was chosen as a balance between the requirements of different platforms. > > > However, this does require that the start address of physical memory is > > > a multiple of 128 MiB, precluding booting Linux on platforms where this > > > requirement is not fulfilled. > > > > > > Fix this limitation by obtaining the start address from the DTB instead, > > > if available (either explicitly passed, or appended to the kernel). > > > Fall back to the traditional method when needed. > > > > > > This allows to boot Linux on r7s9210/rza2mevb using the 64 MiB of SDRAM > > > on the RZA2MEVB sub board, which is located at 0x0C000000 (CS3 space), > > > i.e. not at a multiple of 128 MiB. > > > > > > Suggested-by: Nicolas Pitre <nico@xxxxxxxxxxx> > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > > > Reviewed-by: Nicolas Pitre <nico@xxxxxxxxxxx> > > > Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > > > Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx> > > > Cc: Lukasz Stelmach <l.stelmach@xxxxxxxxxxx> > > > --- > > > Marked as RFC, because: > > > 1. This is known to break crashkernel support, as the memory used by > > > the crashkernel is not marked reserved in DT (yet), > > > 2. Russell won't apply this for v5.9 anyway, > > > > > > > Would it help if we make this behavior dependent on a simple heuristic, e.g., > > > > if (round_up(load_address, 128M) >= dram_end) > > use dram_start from DT > > else > > use round_up(load_address, 128M) > > > > That way, the fix is guaranteed to only take effect for systems that > > cannot even boot otherwise, which fixes the crashkernel case, as well > > as other potential regressions due to the load address of the core > > kernel changing for existing boards. > > Thanks for your suggestion! > 1. Shouldn't the calculation use round_down() instead of round_up()? > 2. Likewise, "round_down(load_address, 128M) < dram_start from DT"? > No. What the code does today is round *up* to a multiple of 128 MB, and only when that leads to a problem, we should use the DT provided memory regions.
