Re: [PATCH v2 13/39] xen/riscv: introduce asm/system.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.11.2023 11:30, Oleksii Kurochko wrote:
> --- /dev/null
> +++ b/xen/arch/riscv/include/asm/system.h
> @@ -0,0 +1,79 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _ASM_RISCV_BARRIER_H
> +#define _ASM_RISCV_BARRIER_H
> +
> +#include <asm/csr.h>
> +
> +#ifndef __ASSEMBLY__
> +
> +#define RISCV_FENCE(p, s) \
> +    __asm__ __volatile__ ("fence " #p "," #s : : : "memory")

Nit (style): Missing blanks immediately inside the parentheses.

> +/* These barriers need to enforce ordering on both devices or memory. */
> +#define mb()                    RISCV_FENCE(iorw,iorw)
> +#define rmb()                   RISCV_FENCE(ir,ir)
> +#define wmb()                   RISCV_FENCE(ow,ow)

Nit (style): Missing blanks after the commas (also again below).

> +/* These barriers do not need to enforce ordering on devices, just memory. */
> +#define smp_mb()                RISCV_FENCE(rw,rw)
> +#define smp_rmb()               RISCV_FENCE(r,r)
> +#define smp_wmb()               RISCV_FENCE(w,w)
> +#define smp_mb__before_atomic() smp_mb()
> +#define smp_mb__after_atomic()  smp_mb()
> +
> +/*
> +#define __smp_store_release(p, v)       \

Is there a need for the double underscores here? We try to not
introduce new instances of undue leading underscores, but there might
be e.g. a strong desire to stay in sync with, say, Linux.

> +do {                                    \
> +     compiletime_assert_atomic_type(*p); \
> +     RISCV_FENCE(rw,w);                  \
> +     WRITE_ONCE(*p, v);                  \

Nit: Can the trailing backslashes be aligned, please?

> +} while (0)
> +
> +#define __smp_load_acquire(p)           \
> +({                                      \
> +    typeof(*p) ___p1 = READ_ONCE(*p);   \

Hmm, yet more leading underscores, and here surely not needed.

> +    compiletime_assert_atomic_type(*p); \
> +    RISCV_FENCE(r,rw);                  \
> +    ___p1;                              \
> +})
> +*/
> +
> +static inline unsigned long local_save_flags(void)
> +{
> +    return csr_read(sstatus);
> +}
> +
> +static inline void local_irq_enable(void)
> +{
> +    csr_set(sstatus, SSTATUS_SIE);
> +}
> +
> +static inline void local_irq_disable(void)
> +{
> +    csr_clear(sstatus, SSTATUS_SIE);
> +}
> +
> +#define local_irq_save(x)                           \
> +({                                                  \
> +    x = csr_read_clear(CSR_SSTATUS, SSTATUS_SIE);   \
> +    local_irq_disable();                            \
> +})
> +
> +static inline void local_irq_restore(unsigned long flags)
> +{
> +     csr_set(CSR_SSTATUS, flags & SSTATUS_SIE);
> +}
> +
> +static inline int local_irq_is_enabled(void)
> +{
> +    unsigned long flags = local_save_flags();
> +
> +    return flags & SSTATUS_SIE;

SSTATUS_SIE doesn't even happen to be 1, so I think you're better off
adding != 0, unless you would do as I think I had suggested before and
have the function return bool right away.

Jan