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hw/char: riscv_htif: Avoid using magic numbers

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The Spike HTIF is poorly documented. The only relevant info we can
get from the internet is from Andrew Waterman at [1].

Add a comment block before htif_handle_tohost_write() to explain
the tohost register format, and use meaningful macros instead of
magic numbers in the codes.

While we are here, correct 2 multi-line comment blocks that have
wrong format.

Link: https://github.com/riscv-software-src/riscv-isa-sim/issues/364#issuecomment-607657754 [1]
Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221229091828.1945072-2-bmeng@tinylab.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
This commit is contained in:
Bin Meng 2022-12-29 17:18:17 +08:00 committed by Alistair Francis
parent 239b8b0699
commit 753ae97abc
1 changed files with 52 additions and 20 deletions
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72
hw/char/riscv_htif.c
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@ -38,6 +38,16 @@
} \
} while (0)
#define HTIF_DEV_SHIFT 56
#define HTIF_CMD_SHIFT 48
#define HTIF_DEV_SYSTEM 0
#define HTIF_DEV_CONSOLE 1
#define HTIF_SYSTEM_CMD_SYSCALL 0
#define HTIF_CONSOLE_CMD_GETC 0
#define HTIF_CONSOLE_CMD_PUTC 1
static uint64_t fromhost_addr, tohost_addr;
static int address_symbol_set;
@ -81,9 +91,11 @@ static void htif_recv(void *opaque, const uint8_t *buf, int size)
return;
}
/* TODO - we need to check whether mfromhost is zero which indicates
the device is ready to receive. The current implementation
will drop characters */
/*
* TODO - we need to check whether mfromhost is zero which indicates
* the device is ready to receive. The current implementation
* will drop characters
*/
uint64_t val_written = htifstate->pending_read;
uint64_t resp = 0x100 | *buf;
@ -110,10 +122,30 @@ static int htif_be_change(void *opaque)
return 0;
}
/*
* See below the tohost register format.
*
* Bits 63:56 indicate the "device".
* Bits 55:48 indicate the "command".
*
* Device 0 is the syscall device, which is used to emulate Unixy syscalls.
* It only implements command 0, which has two subfunctions:
* - If bit 0 is clear, then bits 47:0 represent a pointer to a struct
* describing the syscall.
* - If bit 1 is set, then bits 47:1 represent an exit code, with a zero
* value indicating success and other values indicating failure.
*
* Device 1 is the blocking character device.
* - Command 0 reads a character
* - Command 1 writes a character from the 8 LSBs of tohost
*
* For RV32, the tohost register is zero-extended, so only device=0 and
* command=0 (i.e. HTIF syscalls/exit codes) are supported.
*/
static void htif_handle_tohost_write(HTIFState *htifstate, uint64_t val_written)
{
uint8_t device = val_written >> 56;
uint8_t cmd = val_written >> 48;
uint8_t device = val_written >> HTIF_DEV_SHIFT;
uint8_t cmd = val_written >> HTIF_CMD_SHIFT;
uint64_t payload = val_written & 0xFFFFFFFFFFFFULL;
int resp = 0;
@ -125,9 +157,9 @@ static void htif_handle_tohost_write(HTIFState *htifstate, uint64_t val_written)
* 0: riscv-tests Pass/Fail Reporting Only (no syscall proxy)
* 1: Console
*/
if (unlikely(device == 0x0)) {
if (unlikely(device == HTIF_DEV_SYSTEM)) {
/* frontend syscall handler, shutdown and exit code support */
if (cmd == 0x0) {
if (cmd == HTIF_SYSTEM_CMD_SYSCALL) {
if (payload & 0x1) {
/* exit code */
int exit_code = payload >> 1;
@ -138,14 +170,14 @@ static void htif_handle_tohost_write(HTIFState *htifstate, uint64_t val_written)
} else {
qemu_log("HTIF device %d: unknown command\n", device);
}
} else if (likely(device == 0x1)) {
} else if (likely(device == HTIF_DEV_CONSOLE)) {
/* HTIF Console */
if (cmd == 0x0) {
if (cmd == HTIF_CONSOLE_CMD_GETC) {
/* this should be a queue, but not yet implemented as such */
htifstate->pending_read = val_written;
htifstate->env->mtohost = 0; /* clear to indicate we read */
return;
} else if (cmd == 0x1) {
} else if (cmd == HTIF_CONSOLE_CMD_PUTC) {
qemu_chr_fe_write(&htifstate->chr, (uint8_t *)&payload, 1);
resp = 0x100 | (uint8_t)payload;
} else {
@ -157,15 +189,15 @@ static void htif_handle_tohost_write(HTIFState *htifstate, uint64_t val_written)
" payload: %016" PRIx64, device, cmd, payload & 0xFF, payload);
}
/*
* - latest bbl does not set fromhost to 0 if there is a value in tohost
* - with this code enabled, qemu hangs waiting for fromhost to go to 0
* - with this code disabled, qemu works with bbl priv v1.9.1 and v1.10
* - HTIF needs protocol documentation and a more complete state machine
while (!htifstate->fromhost_inprogress &&
htifstate->env->mfromhost != 0x0) {
}
*/
* Latest bbl does not set fromhost to 0 if there is a value in tohost.
* With this code enabled, qemu hangs waiting for fromhost to go to 0.
* With this code disabled, qemu works with bbl priv v1.9.1 and v1.10.
* HTIF needs protocol documentation and a more complete state machine.
*
* while (!htifstate->fromhost_inprogress &&
* htifstate->env->mfromhost != 0x0) {
* }
*/
htifstate->env->mfromhost = (val_written >> 48 << 48) | (resp << 16 >> 16);
htifstate->env->mtohost = 0; /* clear to indicate we read */
}
@ -196,7 +228,7 @@ static uint64_t htif_mm_read(void *opaque, hwaddr addr, unsigned size)
/* CPU wrote to an HTIF register */
static void htif_mm_write(void *opaque, hwaddr addr,
uint64_t value, unsigned size)
uint64_t value, unsigned size)
{
HTIFState *htifstate = opaque;
if (addr == TOHOST_OFFSET1) {