Re: [PATCH v3 2/4] hw/cxl: Use switch statements for read and write of cachemem registers

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 19, 2023 at 10:34:32AM +0100, Jonathan Cameron wrote:
> Establishing that only register accesses of size 4 and 8 can occur
> using these functions requires looking at their callers. Make it
> easier to see that by using switch statements.
> Assertions are used to enforce that the register storage is of the
> matching size, allowing fixed values to be used for divisors of
> the array indices.
> 
> Suggested-by: Michael Tokarev <mjt@tls.msk.ru>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Fan Ni <fan.ni@samsung.com>
> ---
>  hw/cxl/cxl-component-utils.c | 65 +++++++++++++++++++++++-------------
>  1 file changed, 42 insertions(+), 23 deletions(-)
> 
> diff --git a/hw/cxl/cxl-component-utils.c b/hw/cxl/cxl-component-utils.c
> index f3bbf0fd13..7ef3ef2bd6 100644
> --- a/hw/cxl/cxl-component-utils.c
> +++ b/hw/cxl/cxl-component-utils.c
> @@ -67,16 +67,24 @@ static uint64_t cxl_cache_mem_read_reg(void *opaque, hwaddr offset,
>      CXLComponentState *cxl_cstate = opaque;
>      ComponentRegisters *cregs = &cxl_cstate->crb;
>  
> -    if (size == 8) {
> +    switch (size) {
> +    case 4:
> +        if (cregs->special_ops && cregs->special_ops->read) {
> +            return cregs->special_ops->read(cxl_cstate, offset, 4);
> +        } else {
> +            static_assert(sizeof(*cregs->cache_mem_registers) == 4);

In C currently static_assert needs a message.

In fact clang warns:
../hw/cxl/cxl-component-utils.c:75:67: error: '_Static_assert' with no message is a C2x extension [-Werror,-Wc2x-extensions]
            static_assert(sizeof(*cregs->cache_mem_registers) == 4);


> +            return cregs->cache_mem_registers[offset / 4];
> +        }
> +    case 8:
>          qemu_log_mask(LOG_UNIMP,
>                        "CXL 8 byte cache mem registers not implemented\n");
>          return 0;
> -    }
> -
> -    if (cregs->special_ops && cregs->special_ops->read) {
> -        return cregs->special_ops->read(cxl_cstate, offset, size);
> -    } else {
> -        return cregs->cache_mem_registers[offset / sizeof(*cregs->cache_mem_registers)];
> +    default:
> +        /*
> +         * In line with specifiction limitaions on access sizes, this
> +         * routine is not called with other sizes.
> +         */
> +        g_assert_not_reached();
>      }
>  }
>  
> @@ -117,25 +125,36 @@ static void cxl_cache_mem_write_reg(void *opaque, hwaddr offset, uint64_t value,
>      ComponentRegisters *cregs = &cxl_cstate->crb;
>      uint32_t mask;
>  
> -    if (size == 8) {
> +    switch (size) {
> +    case 4:
> +        static_assert(sizeof(*cregs->cache_mem_regs_write_mask) == 4);
> +        static_assert(sizeof(*cregs->cache_mem_registers) == 4);
> +        mask = cregs->cache_mem_regs_write_mask[offset / 4];
> +        value &= mask;
> +        /* RO bits should remain constant. Done by reading existing value */
> +        value |= ~mask & cregs->cache_mem_registers[offset / 4];
> +        if (cregs->special_ops && cregs->special_ops->write) {
> +            cregs->special_ops->write(cxl_cstate, offset, value, size);
> +            return;
> +        }
> +
> +        if (offset >= A_CXL_HDM_DECODER_CAPABILITY &&
> +            offset <= A_CXL_HDM_DECODER3_TARGET_LIST_HI) {
> +            dumb_hdm_handler(cxl_cstate, offset, value);
> +        } else {
> +            cregs->cache_mem_registers[offset / 4] = value;
> +        }
> +        return;
> +    case 8:
>          qemu_log_mask(LOG_UNIMP,
>                        "CXL 8 byte cache mem registers not implemented\n");
>          return;
> -    }
> -    mask = cregs->cache_mem_regs_write_mask[offset / sizeof(*cregs->cache_mem_regs_write_mask)];
> -    value &= mask;
> -    /* RO bits should remain constant. Done by reading existing value */
> -    value |= ~mask & cregs->cache_mem_registers[offset / sizeof(*cregs->cache_mem_registers)];
> -    if (cregs->special_ops && cregs->special_ops->write) {
> -        cregs->special_ops->write(cxl_cstate, offset, value, size);
> -        return;
> -    }
> -
> -    if (offset >= A_CXL_HDM_DECODER_CAPABILITY &&
> -        offset <= A_CXL_HDM_DECODER3_TARGET_LIST_HI) {
> -        dumb_hdm_handler(cxl_cstate, offset, value);
> -    } else {
> -        cregs->cache_mem_registers[offset / sizeof(*cregs->cache_mem_registers)] = value;
> +    default:
> +        /*
> +         * In line with specifiction limitaions on access sizes, this
> +         * routine is not called with other sizes.
> +         */
> +        g_assert_not_reached();
>      }
>  }
>  
> -- 
> 2.39.2