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    SubjectRe: [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64
    On Wed, Dec 22, 2021 at 1:59 PM Guo Ren <guoren@kernel.org> wrote:
    > On Wed, Dec 22, 2021 at 2:10 AM Arnd Bergmann <arnd@arndb.de> wrote:
    > > On Tue, Dec 21, 2021 at 5:35 PM <guoren@kernel.org> wrote:
    >
    > > There is still some benefit in b), but it would need to be weighed
    > > against the downsides above. Can you explain in more detail what
    > > use cases you have in mind, and which CPU cores actually support
    > > this mode?
    > The most reason is about b), see our customer's product:
    > https://www.cnx-software.com/2021/10/25/allwinner-d1s-f133-risc-v-processor-64mb-ddr2/
    >
    > So I think all our next generation rv64 cores should support
    > compat-mode. Compare to releasing rv32-full core, rv64 compat-mode is
    > very cheap for our CPU design.
    >
    > You would get the answer when our new generation CPU is announced and it's soon.
    >
    > Currently, only qemu supports rv64 compact mode, that is my colleague
    > (LIU Zhi Wei) contributed.

    Right, that does make a lot of sense. I'm not sure we'll see a lot more of 64MB
    DDR2 SiP implementations when a 128MB or even 256MB DDR3 configuration
    has almost the same cost, but for any of those sizes I can see why you'd want to
    run 32-bit user space, as well as 64-bit kernels.

    Arnd

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