It was <2020-05-19 wto 13:21>, when Geert Uytterhoeven wrote: > Hi Russell, > > CC devicetree > > On Tue, May 19, 2020 at 11:46 AM Russell King - ARM Linux admin > <linux@xxxxxxxxxxxxxxx> wrote: >> On Tue, May 19, 2020 at 11:44:17AM +0200, Geert Uytterhoeven wrote: >>> On Tue, May 19, 2020 at 10:54 AM Lukasz Stelmach <l.stelmach@xxxxxxxxxxx> wrote: >>>> It was <2020-04-29 śro 10:21>, when Geert Uytterhoeven 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> >>>>> --- >>>> >>>> [...] >>>> >>>> Apparently reading physical memory layout from DTB breaks crashdump >>>> kernels. A crashdump kernel is loaded into a region of memory, that >>>> is reserved in the original (i.e. to be crashed) kernel. The >>>> reserved region is large enough for the crashdump kernel to run >>>> completely inside it and don't modify anything outside it, just >>>> read and dump the remains of the crashed kernel. Using the >>>> information from DTB makes the decompressor place the kernel >>>> outside of the dedicated region. >>>> >>>> The log below shows that a zImage and DTB are loaded at 0x18eb8000 >>>> and 0x193f6000 (physical). The kernel is expected to run at >>>> 0x18008000, but it is decompressed to 0x00008000 (see r4 reported >>>> before jumping from within __enter_kernel). If I were to suggest >>>> something, there need to be one more bit of information passed in >>>> the DTB telling the decompressor to use the old masking technique >>>> to determain kernel address. It would be set in the DTB loaded >>>> along with the crashdump kernel. >>> >>> Shouldn't the DTB passed to the crashkernel describe which region of >>> memory is to be used instead? >> >> Definitely not. The crashkernel needs to know where the RAM in the >> machine is, so that it can create a coredump of the crashed kernel. > > So the DTB should describe both ;-) So we can do without the mem= cmdline option which is required now. Sounds reasonable to me. -- Łukasz Stelmach Samsung R&D Institute Poland Samsung Electronics
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