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Re: [RFC] hw/registerfields: add `FIELDx_1CLEAR()` macro


From: Alistair Francis
Subject: Re: [RFC] hw/registerfields: add `FIELDx_1CLEAR()` macro
Date: Fri, 23 Sep 2022 14:32:07 +1000

On Thu, Sep 1, 2022 at 11:03 AM Wilfred Mallawa
<wilfred.mallawa@opensource.wdc.com> wrote:
>
> From: Wilfred Mallawa <wilfred.mallawa@wdc.com>
>
> Adds a helper macro that implements the `rw1c`
> behaviour.
>
> Ex:
>   uint32_t data = FIELD32_1CLEAR(val, REG, FIELD);
>
> if the specified `FIELD` is set (single/multi bit all fields)
> then the respective field is cleared and returned to `data`.
>
> If ALL bits of the bitfield are not set, then no change and
> val is returned.

I feel like the value is operating over the entire field.

Say for example there is an interrupt pending register, with a current
value of 0b0010.

If a guest writes 0b1111 they expect ALL of the bits to be cleared
(for a w1c register). I think the macro should handle that, instead of
requiring the exact bits to be set.

Alistair

>
> Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
> ---
>  include/hw/registerfields.h | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/include/hw/registerfields.h b/include/hw/registerfields.h
> index 1330ca77de..5a804f72e3 100644
> --- a/include/hw/registerfields.h
> +++ b/include/hw/registerfields.h
> @@ -115,6 +115,34 @@
>                    R_ ## reg ## _ ## field ## _LENGTH, _v.v);              \
>      _d; })
>
> +/* Get the max value (uint) discribed by `num_bits` bits */
> +#define MAX_N_BITS(num_bits) ((1 << (num_bits)) - 1)
> +
> +/*
> + * Clear the specified field in reg_val if
> + * all field bits are set, else no changes made. Implements
> + * single/multi-bit `rw1c`
> + */
> +#define FIELD8_1CLEAR(reg_val, reg, field)                                \
> +    ((FIELD_EX8(reg_val, reg, field) ==                                   \
> +      MAX_N_BITS(R_ ## reg ## _ ## field ## _LENGTH)) ?                   \
> +      FIELD_DP8(reg_val, reg, field, 0x00) : reg_val)
> +
> +#define FIELD16_1CLEAR(reg_val, reg, field)                               \
> +    ((FIELD_EX16(reg_val, reg, field) ==                                  \
> +      MAX_N_BITS(R_ ## reg ## _ ## field ## _LENGTH)) ?                   \
> +      FIELD_DP16(reg_val, reg, field, 0x00) : reg_val)
> +
> +#define FIELD32_1CLEAR(reg_val, reg, field)                               \
> +    ((FIELD_EX32(reg_val, reg, field) ==                                  \
> +      MAX_N_BITS(R_ ## reg ## _ ## field ## _LENGTH)) ?                   \
> +      FIELD_DP32(reg_val, reg, field, 0x00) : reg_val)
> +
> +#define FIELD64_1CLEAR(reg_val, reg, field)                               \
> +    ((FIELD_EX64(reg_val, reg, field) ==                                  \
> +      MAX_N_BITS(R_ ## reg ## _ ## field ## _LENGTH)) ?                   \
> +      FIELD_DP64(reg_val, reg, field, 0x00) : reg_val)
> +
>  #define FIELD_SDP8(storage, reg, field, val) ({                           \
>      struct {                                                              \
>          signed int v:R_ ## reg ## _ ## field ## _LENGTH;                  \
> --
> 2.37.2
>
>



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