From: Bin Meng <bm...@tinylab.org> 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 <bm...@tinylab.org> Reviewed-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com> Reviewed-by: Alistair Francis <alistair.fran...@wdc.com> Message-Id: <20221229091828.1945072-2-bm...@tinylab.org> Signed-off-by: Alistair Francis <alistair.fran...@wdc.com> --- hw/char/riscv_htif.c | 72 ++++++++++++++++++++++++++++++++------------ 1 file changed, 52 insertions(+), 20 deletions(-) diff --git a/hw/char/riscv_htif.c b/hw/char/riscv_htif.c index 6577f0e640..088556bb04 100644 --- a/hw/char/riscv_htif.c +++ b/hw/char/riscv_htif.c @@ -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) { -- 2.39.0
