Re: [Qemu-devel] [PATCH v5 02/15] register: Add Register API

["Alex Bennée" <alex.bennee@linaro.org>]

Alistair Francis <alistair.francis@xilinx.com> writes:

> This API provides some encapsulation of registers and factors our some
> common functionality to common code. Bits of device state (usually MMIO
> registers), often have all sorts of access restrictions and semantics
> associated with them. This API allow you to define what those
> restrictions are on a bit-by-bit basis.
>
> Helper functions are then used to access the register which observe the
> semantics defined by the RegisterAccessInfo struct.
>
> Some features:
> Bits can be marked as read_only (ro field)
> Bits can be marked as write-1-clear (w1c field)
> Bits can be marked as reserved (rsvd field)
> Reset values can be defined (reset)
> Bits can be marked clear on read (cor)
> Pre and post action callbacks can be added to read and write ops
> Verbose debugging info can be enabled/disabled
>
> Useful for defining device register spaces in a data driven way. Cuts
> down on a lot of the verbosity and repetition in the switch-case blocks
> in the standard foo_mmio_read/write functions.
>
> Also useful for automated generation of device models from hardware
> design sources.
>
> Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
> ---
> V5:
>  - Convert to using only one memory region
> V4:
>  - Rebase
>  - Remove the guest error masking
>  - Simplify the unimplemented masking
>  - Use the reserved value in the write calculations
>  - Remove read_lite and write_lite
>  - General fixes to asserts and log printing
> V3:
>  - Address some comments from Fred
>
>  hw/core/Makefile.objs |   1 +
>  hw/core/register.c    | 148 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/hw/register.h | 108 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 257 insertions(+)
>  create mode 100644 hw/core/register.c
>  create mode 100644 include/hw/register.h
>
> diff --git a/hw/core/Makefile.objs b/hw/core/Makefile.objs
> index abb3560..bf95db5 100644
> --- a/hw/core/Makefile.objs
> +++ b/hw/core/Makefile.objs
> @@ -14,4 +14,5 @@ common-obj-$(CONFIG_SOFTMMU) += machine.o
>  common-obj-$(CONFIG_SOFTMMU) += null-machine.o
>  common-obj-$(CONFIG_SOFTMMU) += loader.o
>  common-obj-$(CONFIG_SOFTMMU) += qdev-properties-system.o
> +common-obj-$(CONFIG_SOFTMMU) += register.o
>  common-obj-$(CONFIG_PLATFORM_BUS) += platform-bus.o
> diff --git a/hw/core/register.c b/hw/core/register.c
> new file mode 100644
> index 0000000..1656f71
> --- /dev/null
> +++ b/hw/core/register.c
> @@ -0,0 +1,148 @@
> +/*
> + * Register Definition API
> + *
> + * Copyright (c) 2016 Xilinx Inc.
> + * Copyright (c) 2013 Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/register.h"
> +#include "hw/qdev.h"
> +#include "qemu/log.h"
> +
> +static inline void register_write_val(RegisterInfo *reg, uint64_t val)
> +{
> +    g_assert(reg->data);
> +
> +    switch (reg->data_size) {
> +    case 1:
> +        *(uint8_t *)reg->data = val;
> +        break;
> +    case 2:
> +        *(uint16_t *)reg->data = val;
> +        break;
> +    case 4:
> +        *(uint32_t *)reg->data = val;
> +        break;
> +    case 8:
> +        *(uint64_t *)reg->data = val;
> +        break;
> +    default:
> +        g_assert_not_reached();
> +    }
> +}
> +
> +static inline uint64_t register_read_val(RegisterInfo *reg)
> +{
> +    switch (reg->data_size) {
> +    case 1:
> +        return *(uint8_t *)reg->data;
> +    case 2:
> +        return *(uint16_t *)reg->data;
> +    case 4:
> +        return *(uint32_t *)reg->data;
> +    case 8:
> +        return *(uint64_t *)reg->data;
> +    default:
> +        g_assert_not_reached();
> +    }
> +    return 0; /* unreachable */
> +}
> +
> +void register_write(RegisterInfo *reg, uint64_t val, uint64_t we)
> +{
> +    uint64_t old_val, new_val, test, no_w_mask;
> +    const RegisterAccessInfo *ac;
> +
> +    assert(reg);
> +
> +    ac = reg->access;
> +
> +    if (!ac || !ac->name) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "%s: write to undefined device state "
> +                      "(written value: %#" PRIx64 ")\n", reg->prefix, val);
> +        return;
> +    }
> +
> +    old_val = reg->data ? register_read_val(reg) : ac->reset;
> +
> +    test = (old_val ^ val) & ac->rsvd;
> +    if (test) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "%s: change of value in reserved bit"
> +                      "fields: %#" PRIx64 ")\n", reg->prefix, test);
> +    }
> +
> +    test = val & ac->unimp;
> +    if (test) {
> +        qemu_log_mask(LOG_UNIMP,
> +                      "%s:%s writing %#" PRIx64 " to unimplemented bits:" \
> +                      " %#" PRIx64 "",
> +                      reg->prefix, reg->access->name, val, ac->unimp);
> +    }
> +
> +    /* Create the no write mask based on the read only, write to clear and
> +     * reserved bit masks.
> +     */
> +    no_w_mask = ac->ro | ac->w1c | ac->rsvd | ~we;
> +    new_val = (val & ~no_w_mask) | (old_val & no_w_mask);
> +    new_val &= ~(val & ac->w1c);
> +
> +    if (ac->pre_write) {
> +        new_val = ac->pre_write(reg, new_val);
> +    }
> +
> +    if (reg->debug) {
> +        qemu_log("%s:%s: write of value %#" PRIx64 "\n", reg->prefix, ac->name,
> +                 new_val);
> +    }
> +
> +    register_write_val(reg, new_val);
> +
> +    if (ac->post_write) {
> +        ac->post_write(reg, new_val);
> +    }
> +}
> +
> +uint64_t register_read(RegisterInfo *reg)
> +{
> +    uint64_t ret;
> +    const RegisterAccessInfo *ac;
> +
> +    assert(reg);
> +
> +    ac = reg->access;
> +    if (!ac || !ac->name) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "%s: read from undefined device state\n",
> +                      reg->prefix);
> +        return 0;
> +    }
> +
> +    ret = reg->data ? register_read_val(reg) : ac->reset;
> +
> +    register_write_val(reg, ret & ~ac->cor);
> +
> +    if (ac->post_read) {
> +        ret = ac->post_read(reg, ret);
> +    }
> +
> +    if (reg->debug) {
> +        qemu_log("%s:%s: read of value %#" PRIx64 "\n", reg->prefix,
> +                 ac->name, ret);
> +    }
> +
> +    return ret;
> +}
> +
> +void register_reset(RegisterInfo *reg)
> +{
> +    g_assert(reg);
> +
> +    if (!reg->data || !reg->access) {
> +        return;
> +    }
> +
> +    register_write_val(reg, reg->access->reset);
> +}
> diff --git a/include/hw/register.h b/include/hw/register.h
> new file mode 100644
> index 0000000..baa08f5
> --- /dev/null
> +++ b/include/hw/register.h
> @@ -0,0 +1,108 @@
> +/*
> + * Register Definition API
> + *
> + * Copyright (c) 2016 Xilinx Inc.
> + * Copyright (c) 2013 Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + */
> +
> +#ifndef REGISTER_H
> +#define REGISTER_H
> +
> +#include "exec/memory.h"
> +
> +typedef struct RegisterInfo RegisterInfo;
> +typedef struct RegisterAccessInfo RegisterAccessInfo;
> +
> +/**
> + * Access description for a register that is part of guest accessible device
> + * state.
> + *
> + * @name: String name of the register
> + * @ro: whether or not the bit is read-only
> + * @w1c: bits with the common write 1 to clear semantic.
> + * @reset: reset value.
> + * @cor: Bits that are clear on read
> + * @rsvd: Bits that are reserved and should not be changed
> + *
> + * @pre_write: Pre write callback. Passed the value that's to be written,
> + * immediately before the actual write. The returned value is what is written,
> + * giving the handler a chance to modify the written value.
> + * @post_write: Post write callback. Passed the written value. Most write side
> + * effects should be implemented here.
> + *
> + * @post_read: Post read callback. Passes the value that is about to be returned
> + * for a read. The return value from this function is what is ultimately read,
> + * allowing this function to modify the value before return to the client.
> + */
> +
> +struct RegisterAccessInfo {
> +    const char *name;
> +    uint64_t ro;
> +    uint64_t w1c;
> +    uint64_t reset;
> +    uint64_t cor;
> +    uint64_t rsvd;
> +    uint64_t unimp;
> +
> +    uint64_t (*pre_write)(RegisterInfo *reg, uint64_t val);
> +    void (*post_write)(RegisterInfo *reg, uint64_t val);
> +
> +    uint64_t (*post_read)(RegisterInfo *reg, uint64_t val);
> +};
> +
> +/**
> + * A register that is part of guest accessible state
> + * @data: pointer to the register data. Will be cast
> + * to the relevant uint type depending on data_size.
> + * @data_size: Size of the register in bytes. Must be
> + * 1, 2, 4 or 8
> + *
> + * @access: Access description of this register
> + *
> + * @debug: Whether or not verbose debug is enabled
> + * @prefix: String prefix for log and debug messages
> + *
> + * @opaque: Opaque data for the register
> + */
> +
> +struct RegisterInfo {
> +    /* <public> */
> +    void *data;
> +    int data_size;
> +
> +    const RegisterAccessInfo *access;
> +
> +    bool debug;
> +    const char *prefix;
> +
> +    void *opaque;
> +};
> +
> +/**
> + * write a value to a register, subject to its restrictions
> + * @reg: register to write to
> + * @val: value to write
> + * @we: write enable mask
> + */
> +
> +void register_write(RegisterInfo *reg, uint64_t val, uint64_t we);
> +
> +/**
> + * read a value from a register, subject to its restrictions
> + * @reg: register to read from
> + * returns: value read
> + */
> +
> +uint64_t register_read(RegisterInfo *reg);
> +
> +/**
> + * reset a register
> + * @reg: register to reset
> + */
> +
> +void register_reset(RegisterInfo *reg);
> +
> +#endif

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

--
Alex Bennée