On Tue, Dec 27, 2022 at 4:50 PM Bin Meng <bm...@tinylab.org> wrote:
>
> 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 intead of
> magic numbers in the codes.
>
> While we are here, corret 2 multi-line comment blocks that have
> wrong format.
>
> Link: https://github.com/riscv-software-src/riscv-isa-sim/issues/364 [1]
> Signed-off-by: Bin Meng <bm...@tinylab.org>
Reviewed-by: Alistair Francis <alistair.fran...@wdc.com>
Alistair
> ---
>
> 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) {
> --
> 2.34.1
>
>
