Re: [PATCH 5/6] hw/arm/xilinx_zynq: Remove tswap32() calls and constify smpboot[]

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Thu, Dec 22, 2022 at 10:55:48PM +0100, Philippe Mathieu-Daudé wrote:
> ARM CPUs fetch instructions in little-endian.
> 
> smpboot[] encoded instructions are written in little-endian.
> 
> We call tswap32() on the array. tswap32 function swap a 32-bit
> value if the target endianness doesn't match the host one.
> Otherwise it is a NOP.
> 
> * On a little-endian host, the array is stored as it. tswap32()
>   is a NOP, and the vCPU fetches the instructions as it, in
>   little-endian.
> 
> * On a big-endian host, the array is stored as it. tswap32()
>   swap the instructions to little-endian, and the vCPU fetches
>   the instructions as it, in little-endian.
> 
> Using tswap() on system emulation is a bit odd: while the target
> particularities might change the system emulation, the host ones
> (such its endianness) shouldn't interfere.
> 
> We can simplify by using const_le32() to always store the
> instructions in the array in little-endian, removing the need
> for the dubious tswap().


Hi Philippe,


> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  hw/arm/xilinx_zynq.c | 27 ++++++++++++---------------
>  1 file changed, 12 insertions(+), 15 deletions(-)
> 
> diff --git a/hw/arm/xilinx_zynq.c b/hw/arm/xilinx_zynq.c
> index 3190cc0b8d..4316143b71 100644
> --- a/hw/arm/xilinx_zynq.c
> +++ b/hw/arm/xilinx_zynq.c
> @@ -71,6 +71,11 @@ static const int dma_irqs[8] = {
>  
>  #define ZYNQ_SDHCI_CAPABILITIES 0x69ec0080  /* Datasheet: UG585 (v1.12.1) */
>  
> +struct ZynqMachineState {
> +    MachineState parent;
> +    Clock *ps_clk;
> +};
> +
>  #define ARMV7_IMM16(x) (extract32((x),  0, 12) | \
>                          extract32((x), 12,  4) << 16)
>  
> @@ -79,29 +84,21 @@ static const int dma_irqs[8] = {
>   */
>  
>  #define SLCR_WRITE(addr, val) \
> -    0xe3001000 + ARMV7_IMM16(extract32((val),  0, 16)), /* movw r1 ... */ \
> -    0xe3401000 + ARMV7_IMM16(extract32((val), 16, 16)), /* movt r1 ... */ \
> -    0xe5801000 + (addr)
> -
> -struct ZynqMachineState {
> -    MachineState parent;
> -    Clock *ps_clk;
> -};
> +    cpu_to_le32(0xe3001000 + ARMV7_IMM16(extract32((val),  0, 16))), /* movw r1 ... */ \
> +    cpu_to_le32(0xe3401000 + ARMV7_IMM16(extract32((val), 16, 16))), /* movt r1 ... */ \

Looks like the callers all pass in constants, perhaps const_le32 should be used everywhere or am I missing something?


> +    const_le32(0xe5801000 + (addr))
>  
>  static void zynq_write_board_setup(ARMCPU *cpu,
>                                     const struct arm_boot_info *info)
>  {
> -    int n;
> -    uint32_t board_setup_blob[] = {
> -        0xe3a004f8, /* mov r0, #0xf8000000 */
> +    const uint32_t board_setup_blob[] = {
> +        const_le32(0xe3a004f8),         /* mov r0, #0xf8000000 */
>          SLCR_WRITE(SLCR_UNLOCK_OFFSET, SLCR_XILINX_UNLOCK_KEY),
>          SLCR_WRITE(SLCR_ARM_PLL_OFFSET, 0x00014008),
>          SLCR_WRITE(SLCR_LOCK_OFFSET, SLCR_XILINX_LOCK_KEY),
> -        0xe12fff1e, /* bx lr */
> +        const_le32(0xe12fff1e)          /* bx lr */
>      };
> -    for (n = 0; n < ARRAY_SIZE(board_setup_blob); n++) {
> -        board_setup_blob[n] = tswap32(board_setup_blob[n]);
> -    }
> +
>      rom_add_blob_fixed("board-setup", board_setup_blob,
>                         sizeof(board_setup_blob), BOARD_SETUP_ADDR);
>  }
> -- 
> 2.38.1
>