On Wed, Dec 22, 2021 at 1:59 PM Guo Ren <guoren@xxxxxxxxxx> wrote: > On Wed, Dec 22, 2021 at 2:10 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Tue, Dec 21, 2021 at 5:35 PM <guoren@xxxxxxxxxx> 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
