Re: [Qemu-devel] [PATCH v2 02/16] register: Add Register API

[Alistair Francis]

On Wed, Jan 27, 2016 at 6:46 AM, KONRAD Frederic
<address@hidden> wrote:
> Hi,
>
>
> Le 19/01/2016 23:34, Alistair Francis a écrit :
>>
>> From: Peter Crosthwaite <address@hidden>
>>
>> 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 throw guest errors when written certain values (ge0, ge1)
>> Bits can throw unimp errors when written certain values (ui0, ui1)
>> 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 <address@hidden>
>> Signed-off-by: Alistair Francis <address@hidden>
>> ---
>> changed from v2:
>> Simplified! Removed pre-read, nwx, wo
>> Removed byte loops (Gerd Review)
>> Made data pointer optional
>> Added fast paths for simple registers
>> Moved into hw/core and include/hw (Paolo Review)
>> changed from v1:
>> Rebranded as the "Register API" - I think thats probably what it is.
>> Near total rewrite of implementation.
>> De-arrayified reset (this is client/Memory APIs job).
>> Moved out of bitops into its own file (Blue review)
>> Added debug, the register pointer, and prefix to a struct (Blue Review)
>> Made 64-bit to play friendlier with memory API (Blue review)
>> Made backend storage uint8_t (MST review)
>> Added read/write callbacks (Blue review)
>> Added ui0, ui1 (Blue review)
>> Moved re-purposed width (now byte width defining actual storage size)
>> Arrayified ge0, ge1 (ui0, ui1 too) and added .reason
>> Added wo field (not an April fools joke - this has genuine meaning here)
>> Added we mask to write accessor
>>
>>   hw/core/Makefile.objs |   1 +
>>   hw/core/register.c    | 186
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>>   include/hw/register.h | 132 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 319 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..02a4376
>> --- /dev/null
>> +++ b/hw/core/register.c
>> @@ -0,0 +1,186 @@
>> +/*
>> + * Register Definition API
>> + *
>> + * Copyright (c) 2013 Xilinx Inc.
>> + * Copyright (c) 2013 Peter Crosthwaite <address@hidden>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2.  See
>> + * the COPYING file in the top-level directory.
>> + */
>> +
>> +#include "hw/register.h"
>> +#include "qemu/log.h"
>> +
>> +static inline void register_write_log(RegisterInfo *reg, int dir,
>> uint64_t val,
>> +                                      int mask, const char *msg,
>> +                                      const char *reason)
>> +{
>> +    qemu_log_mask(mask, "%s:%s bits %#" PRIx64 " %s write of %d%s%s\n",
>> +                  reg->prefix, reg->access->name, val, msg, dir,
>> +                  reason ? ": " : "", reason ? reason : "");
>> +}
>> +
>> +static inline void register_write_val(RegisterInfo *reg, uint64_t val)
>> +{
>> +    if (!reg->data) {
>> +        return;
>> +    }
>> +    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:
>> +        abort();
>> +    }
>> +}
>> +
>> +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:
>> +        abort();
>> +    }
>> +    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;
>> +    const RegisterAccessError *rae;
>> +
>> +    assert(reg);
>> +
>> +    ac = reg->access;
>> +    old_val = reg->data ? register_read_val(reg) : ac->reset;
>
> Don't you need to check ac before doing that?

You are right, I have changed the order.

>
>
>> +    if (reg->write_lite && !~we) { /* fast path!! */
>> +        new_val = val;
>> +        goto register_write_fast;
>> +    }
>> +
>> +    if (!ac || !ac->name) {
>> +        qemu_log_mask(LOG_GUEST_ERROR, "%s: write to undefined device
>> state "
>> +                      "(written value: %#" PRIx64 ")\n", reg->prefix,
>> val);
>> +        return;
>> +    }
>> +
>> +    no_w_mask = ac->ro | ac->w1c | ~we;
>> +
>> +    if (reg->debug) {
>> +        qemu_log("%s:%s: write of value %#" PRIx64 "\n", reg->prefix,
>> ac->name,
>> +                 val);
>> +    }
>> +
>> +    if (qemu_loglevel_mask(LOG_GUEST_ERROR)) {
>> +        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);
>> +        }
>> +        for (rae = ac->ge1; rae && rae->mask; rae++) {
>> +            test = val & rae->mask;
>> +            if (test) {
>> +                register_write_log(reg, 1, test, LOG_GUEST_ERROR,
>> +                                   "invalid", rae->reason);
>> +            }
>> +        }
>> +        for (rae = ac->ge0; rae && rae->mask; rae++) {
>> +            test = ~val & rae->mask;
>> +            if (test) {
>> +                register_write_log(reg, 0, test, LOG_GUEST_ERROR,
>> +                                   "invalid", rae->reason);
>> +            }
>> +        }
>> +    }
>> +
>> +    if (qemu_loglevel_mask(LOG_UNIMP)) {
>> +        for (rae = ac->ui1; rae && rae->mask; rae++) {
>> +            test = val & rae->mask;
>> +            if (test) {
>> +                register_write_log(reg, 1, test, LOG_GUEST_ERROR,
>> +                                   "unimplmented", rae->reason);
>> +            }
>> +        }
>> +        for (rae = ac->ui0; rae && rae->mask; rae++) {
>> +            test = ~val & rae->mask;
>> +            if (test) {
>> +                register_write_log(reg, 0, test, LOG_GUEST_ERROR,
>> +                                   "unimplemented", rae->reason);
>> +            }
>> +        }
>> +    }
>> +
>> +    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);
>> +    }
>> +register_write_fast:
>> +    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;
>> +
>> +    if (!reg->read_lite) {
>> +        register_write_val(reg, ret & ~ac->cor);
>> +    }
>> +
>> +    if (ac->post_read) {
>> +        ret = ac->post_read(reg, ret);
>> +    }
>> +
>> +    if (!reg->read_lite) {
>> +        if (reg->debug) {
>> +            qemu_log("%s:%s: read of value %#" PRIx64 "\n", reg->prefix,
>> +                     ac->name, ret);
>> +        }
>> +    }
>> +
>> +    return ret;
>> +}
>> +
>> +void register_reset(RegisterInfo *reg)
>> +{
>> +    assert(reg);
>> +
>> +    if (!reg->data || !reg->access) {
>> +        return;
>> +    }
>> +
>> +    register_write_val(reg, reg->access->reset);
>> +}
>
> Will that be called systematically at the reset?
> If it is the case what about the register we don't want to reset?

This is called for each register, so if you don't want to reset the
register you don't need to call it for that register.

>
>
>> diff --git a/include/hw/register.h b/include/hw/register.h
>> new file mode 100644
>> index 0000000..249f458
>> --- /dev/null
>> +++ b/include/hw/register.h
>> @@ -0,0 +1,132 @@
>> +/*
>> + * Register Definition API
>> + *
>> + * Copyright (c) 2013 Xilinx Inc.
>> + * Copyright (c) 2013 Peter Crosthwaite <address@hidden>
>> + *
>> + * 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;
>> +
>> +/**
>> + * A register access error message
>> + * @mask: Bits in the register the error applies to
>> + * @reason: Reason why this access is an error
>> + */
>> +
>> +typedef struct RegisterAccessError {
>> +    uint64_t mask;
>> +    const char *reason;
>> +} RegisterAccessError;
>> +
>> +/**
>> + * 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
>> + *
>> + * @ge1: Bits that when written 1 indicate a guest error
>> + * @ge0: Bits that when written 0 indicate a guest error
>> + * @ui1: Bits that when written 1 indicate use of an unimplemented
>> feature
>> + * @ui0: Bits that when written 0 indicate use of an unimplemented
>> feature
>> + *
>> + * @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;
>> +
>> +    const RegisterAccessError *ge0;
>> +    const RegisterAccessError *ge1;
>> +    const RegisterAccessError *ui0;
>> +    const RegisterAccessError *ui1;
>> +
>> +    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 desciption of this register
>
> description

Thanks,

Alistair

>
> Fred
>
>> + *
>> + * @debug: Whether or not verbose debug is enabled
>> + * @prefix: String prefix for log and debug messages
>> + *
>> + * @opaque: Opaque data for the register
>> + */
>> +
>> +struct RegisterInfo {
>> +    void *data;
>> +    int data_size;
>> +
>> +    const RegisterAccessInfo *access;
>> +
>> +    bool debug;
>> +    const char *prefix;
>> +
>> +    void *opaque;
>> +
>> +    /*< private >*/
>> +
>> +    bool read_lite;
>> +    bool write_lite;
>> +};
>> +
>> +/**
>> + * 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
>
>
>