Re: [PATCH v1] mips/mips_malta: Allow more than 2G RAM

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Please post new patches as v2, and do not post them as reply to v1.

On 3/3/20 1:41 AM, Jiaxun Yang wrote:
> When malta is coupled with MIPS64 cpu which have 64bit
> address space, it is possible to have more than 2G RAM.
> 
> So we removed ram_size check and overwrite memory
> layout for these targets.
> 
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> Suggested-by: Yunqiang Su <ysu@wavecomp.com>
> --
> v1: Do not overwrite cmdline when we don't have highmem.
> ---
>   hw/mips/mips_malta.c | 29 +++++++++++++++++++++++------
>   1 file changed, 23 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
> index 6e7ba9235d..4267958f35 100644
> --- a/hw/mips/mips_malta.c
> +++ b/hw/mips/mips_malta.c
> @@ -98,7 +98,8 @@ typedef struct {
>   } MaltaState;
>   
>   static struct _loaderparams {
> -    int ram_size, ram_low_size;
> +    unsigned int ram_low_size;
> +    ram_addr_t ram_size;
>       const char *kernel_filename;
>       const char *kernel_cmdline;
>       const char *initrd_filename;
> @@ -1023,6 +1024,7 @@ static int64_t load_kernel(void)
>   {
>       int64_t kernel_entry, kernel_high, initrd_size;
>       long kernel_size;
> +    char mem_cmdline[128];
>       ram_addr_t initrd_offset;
>       int big_endian;
>       uint32_t *prom_buf;
> @@ -1099,20 +1101,33 @@ static int64_t load_kernel(void)
>       prom_buf = g_malloc(prom_size);
>   
>       prom_set(prom_buf, prom_index++, "%s", loaderparams.kernel_filename);
> +
> +    memset(&mem_cmdline[0], 0, sizeof(mem_cmdline));
> +    if (loaderparams.ram_size > 0x10000000) {

Please use 256 * MiB.

> +        /*
> +         * Always use cmdline to overwrite mem layout
> +         * as kernel may reject large emesize.
> +         */
> +        sprintf(&mem_cmdline[0],
> +                "mem=0x10000000@0x00000000 mem=0x%" PRIx64 "@0x90000000",
> +                loaderparams.ram_size - 0x10000000);

Ditto.

Also please use g_strdup_printf("mem=0x%" PRIx64 "@...")/g_free.

> +    }
> +
>       if (initrd_size > 0) {
>           prom_set(prom_buf, prom_index++,
> -                 "rd_start=0x%" PRIx64 " rd_size=%" PRId64 " %s",
> -                 xlate_to_kseg0(NULL, initrd_offset),
> +                 "%s rd_start=0x%" PRIx64 " rd_size=%" PRId64 " %s",
> +                 &mem_cmdline[0], xlate_to_kseg0(NULL, initrd_offset),
>                    initrd_size, loaderparams.kernel_cmdline);
>       } else {
> -        prom_set(prom_buf, prom_index++, "%s", loaderparams.kernel_cmdline);
> +        prom_set(prom_buf, prom_index++, "%s %s", &mem_cmdline[0],
> +                 loaderparams.kernel_cmdline);
>       }
>   
>       prom_set(prom_buf, prom_index++, "memsize");
>       prom_set(prom_buf, prom_index++, "%u", loaderparams.ram_low_size);
>   
>       prom_set(prom_buf, prom_index++, "ememsize");
> -    prom_set(prom_buf, prom_index++, "%u", loaderparams.ram_size);
> +    prom_set(prom_buf, prom_index++, "%lu", loaderparams.ram_size);
>   
>       prom_set(prom_buf, prom_index++, "modetty0");
>       prom_set(prom_buf, prom_index++, "38400n8r");
> @@ -1253,12 +1268,14 @@ void mips_malta_init(MachineState *machine)
>       /* create CPU */
>       mips_create_cpu(machine, s, &cbus_irq, &i8259_irq);
>   
> -    /* allocate RAM */
> +#ifdef TARGET_MIPS32
> +    /* MIPS32 won't accept more than 2GiB RAM due to limited address space */

Cc'ing Paul Burton due to commit 94c2b6aff43.

>       if (ram_size > 2 * GiB) {
>           error_report("Too much memory for this machine: %" PRId64 "MB,"
>                        " maximum 2048MB", ram_size / MiB);

This is annoying, because the CoreLV/CoreFPGA core cards only have 4 
DIMM slots for PC-100 SDRAM, and the Memory Controller of the GT–64120A 
north bridge accept at most 256 MiB per SCS for address decoding, so we 
have a maximum of 1 GiB on 32-bit boards.

In 64-bit emulation we use the a 20Kc core, provided by the Core20K core 
card which doesn't use the GT–64120A but the Bonito64. So the model is 
incorrect... The Bonito64 indeed allow more memory.

Maybe it is time to consider that for 64-bit targets, since we are not 
modelling a Malta core board, we can name it the official 'virt' machine...

>           exit(1);
>       }
> +#endif
>   
>       /* register RAM at high address where it is undisturbed by IO */
>       memory_region_add_subregion(system_memory, 0x80000000, machine->ram);
>