On Mon, Jan 4, 2021 at 2:01 PM 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 validating the masked address against the memory > information in the passed DTB. Only use the start address > from DTB when masking would yield an out-of-range address, prefer the > traditional method in all other cases. Note that this applies only to the > explicitly passed DTB on modern systems, and not to a DTB appended to > the kernel, or to ATAGS. The appended DTB may need to be augmented by > information from ATAGS, which may need to rely on knowledge of the start > address of physical memory itself. > > 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> > Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > Acked-by: Nicolas Pitre <nico@xxxxxxxxxxx> Sorry for the long delay in reading the patch :( I really like the looks of this now, moreover it is very useful. I suppose it is already in the patch tracker, but for the record: Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > + reg = fdt_getprop(fdt, offset, "linux,usable-memory", &len); I suppose we already had a discussion of why this property is undocumented? Or should we document it? Obviously it is already in widespread use. Yours, Linus Walleij
