Re: [Qemu-devel] [PATCH v3 06/14] sam460ex: Don't size flash memory to match backing image

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

On 3/7/19 2:03 PM, Markus Armbruster wrote:
> Machine "sam460ex" maps its flash memory at address 0xFFF00000.  When
> no image is supplied, its size is 1MiB (0x100000), and 512KiB of ROM
> get mapped on top of its second half.  Else, it's the size of the
> image rounded up to the next multiple of 64KiB.
> 
> The rounding is actually useless: pflash_cfi01_realize() fails with
> "failed to read the initial flash content" unless it's a no-op.
> 
> I have no idea what happens when the pflash's size exceeds 1MiB.
> Useful outcomes seem unlikely.

You now have! [*] "Hardwiring address lines leaves part of the hardware
unaddressable." Anything bigger than 1MiB mapped at 0xFFF00000 only has
the first MiB addressable. IOW anything above 1MiB is unaddressable, but
you still can map a such bigger flash.

[*] https://lists.gnu.org/archive/html/qemu-devel/2019-03/msg01380.html

> I guess memory at the end of the address space remains unmapped when
> it's smaller than 1MiB.  Again, useful outcomes seem unlikely.
> 
> The physical hardware appears to have 512KiB of flash memory:
> https://eu.mouser.com/datasheet/2/268/atmel_AT49BV040B-1180330.pdf
> 
> For now, just set the flash memory size to 1MiB regardless of image
> size, and document the mess.
> 
> Cc: BALATON Zoltan <balaton@eik.bme.hu>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  hw/ppc/sam460ex.c | 41 ++++++++++++++++++++++++++---------------
>  1 file changed, 26 insertions(+), 15 deletions(-)
> 
> diff --git a/hw/ppc/sam460ex.c b/hw/ppc/sam460ex.c
> index d455c4bd07..c6258ca1d0 100644
> --- a/hw/ppc/sam460ex.c
> +++ b/hw/ppc/sam460ex.c
> @@ -91,32 +91,43 @@ struct boot_info {
>  
>  static int sam460ex_load_uboot(void)
>  {
> +    /*
> +     * This first creates 1MiB of flash memory mapped at the end of
> +     * the 32-bit address space (0xFFF00000..0xFFFFFFFF).
> +     *
> +     * If_PFLASH unit 0 is defined, the flash memory is initialized
> +     * from that block backend.
> +     *
> +     * Else, it's initialized to zero.  And then 512KiB of ROM get
> +     * mapped on top of its second half (0xFFF80000..0xFFFFFFFF),
> +     * initialized from u-boot-sam460-20100605.bin.
> +     *
> +     * This doesn't smell right.
> +     *
> +     * The physical hardware appears to have 512KiB flash memory.
> +     *
> +     * TODO Figure out what we really need here, and clean this up.
> +     */
> +
>      DriveInfo *dinfo;
> -    BlockBackend *blk = NULL;
> -    hwaddr base = FLASH_BASE | ((hwaddr)FLASH_BASE_H << 32);
> -    long bios_size = FLASH_SIZE;
> -    int fl_sectors;
>  
>      dinfo = drive_get(IF_PFLASH, 0, 0);
> -    if (dinfo) {
> -        blk = blk_by_legacy_dinfo(dinfo);
> -        bios_size = blk_getlength(blk);
> -    }
> -    fl_sectors = (bios_size + 65535) >> 16;
> -
> -    if (!pflash_cfi01_register(base, NULL, "sam460ex.flash", bios_size,
> -                               blk, 64 * KiB, fl_sectors,
> +    if (!pflash_cfi01_register(FLASH_BASE | ((hwaddr)FLASH_BASE_H << 32),
> +                               NULL, "sam460ex.flash", FLASH_SIZE,
> +                               dinfo ? blk_by_legacy_dinfo(dinfo) : NULL,
> +                               64 * KiB, FLASH_SIZE / (64 * KiB),
>                                 1, 0x89, 0x18, 0x0000, 0x0, 1)) {
>          error_report("Error registering flash memory");
>          /* XXX: return an error instead? */
>          exit(1);
>      }
>  
> -    if (!blk) {
> +    if (!dinfo) {
>          /*error_report("No flash image given with the 'pflash' parameter,"
>                  " using default u-boot image");*/
> -        base = UBOOT_LOAD_BASE | ((hwaddr)FLASH_BASE_H << 32);
> -        rom_add_file_fixed(UBOOT_FILENAME, base, -1);
> +        rom_add_file_fixed(UBOOT_FILENAME,
> +                           UBOOT_LOAD_BASE | ((hwaddr)FLASH_BASE_H << 32),
> +                           -1);
>      }
>  
>      return 0;
>