i'm kind of outdoors now, away from the raspi 4. I didn't find my
   bled112 dongles. here is a draft:
   diff --git a/tools/hciattach.c b/tools/hciattach.c
   index 276a4e56e..c5f3c7462 100644
   --- a/tools/hciattach.c
   +++ b/tools/hciattach.c
   @@ -38,6 +38,30 @@

    #include "hciattach.h"

   +void hex(int pfx, int fd, int buf, int len) {
   + while (len > 0) {
   + fprintf(stderr, "%s %d", pfx, fd);
   + for (int i = 0; i < len && i < 16; i ++) {
   + fprintf(stderr, " %02x", buf[i]);
   + }
   + fprintf(stderr, "\n")
   + len -= 16;
   + buf -= 16;
   + }
   +}
   +
   +int dbg_read(int fd, int buf, int len) {
   + int r = read(fd, buf, len);
   + hex("<", fd, buf, r);
   + return r;
   +}
   +
   +int dbg_write(int fd, int buf, int len) {
   + int r = write(fd, buf, len);
   + hex(">", fd, buf, r);
   + return r;
   +}
   +
    struct uart_t {
     char *type;
     int  m_id;
   @@ -102,7 +126,7 @@ int read_hci_event(int fd, unsigned char* buf, int
   size)
     /* The first byte identifies the packet type. For HCI event packets,
   it
     * should be 0x04, so we read until we get to the 0x04. */
     while (1) {
   - r = read(fd, buf, 1);
   + r = dbg_read(fd, buf, 1);
     if (r <= 0)
     return -1;
     if (buf[0] == 0x04)
   @@ -112,7 +136,7 @@ int read_hci_event(int fd, unsigned char* buf, int
   size)

     /* The next two bytes are the event code and parameter total length.
   */
     while (count < 3) {
   - r = read(fd, buf + count, 3 - count);
   + r = dbg_read(fd, buf + count, 3 - count);
     if (r <= 0)
     return -1;
     count += r;
   @@ -125,7 +149,7 @@ int read_hci_event(int fd, unsigned char* buf, int
   size)
     remain = size - 3;

     while ((count - 3) < remain) {
   - r = read(fd, buf + count, remain - (count - 3));
   + r = dbg_read(fd, buf + count, remain - (count - 3));
     if (r <= 0)
     return -1;
     count += r;
   @@ -180,7 +204,7 @@ static int ericsson(int fd, struct uart_t *u,
   struct termios *ti)
     }

     /* Send initialization command */
   - if (write(fd, cmd, 5) != 5) {
   + if (dbg_write(fd, cmd, 5) != 5) {
     perror("Failed to write init command");
     return -1;
     }
   @@ -217,7 +241,7 @@ static int digi(int fd, struct uart_t *u, struct
   termios *ti)
     }

     /* Send initialization command */
   - if (write(fd, cmd, 5) != 5) {
   + if (dbg_write(fd, cmd, 5) != 5) {
     perror("Failed to write init command");
     return -1;
     }
   @@ -271,7 +295,7 @@ static int read_check(int fd, void *buf, int count)
     int res;

     do {
   - res = read(fd, buf, count);
   + res = dbg_read(fd, buf, count);
     if (res != -1) {
     buf += res;
     count -= res;
   @@ -297,7 +321,7 @@ static void bcsp_tshy_sig_alarm(int sig)

     if (retries < bcsp_max_retries) {
     retries++;
   - if (write(serial_fd, &bcsp_sync_pkt, 10) < 0)
   + if (dbg_write(serial_fd, &bcsp_sync_pkt, 10) < 0)
     return;
     alarm(1);
     return;
   @@ -315,7 +339,7 @@ static void bcsp_tconf_sig_alarm(int sig)

     if (retries < bcsp_max_retries){
     retries++;
   - if (write(serial_fd, &bcsp_conf_pkt, 10) < 0)
   + if (dbg_write(serial_fd, &bcsp_conf_pkt, 10) < 0)
     return;
     alarm(1);
     return;
   @@ -393,7 +417,7 @@ static int bcsp(int fd, struct uart_t *u, struct
   termios *ti)
     }

     if (!memcmp(bcspp, bcspsync, 4)) {
   - if (write(fd, &bcsp_sync_resp_pkt,10) < 0)
   + if (dbg_write(fd, &bcsp_sync_resp_pkt,10) < 0)
     return -1;
     } else if (!memcmp(bcspp, bcspsyncresp, 4))
     break;
   @@ -438,9 +462,9 @@ static int bcsp(int fd, struct uart_t *u, struct
   termios *ti)
     }

     if (!memcmp(bcspp, bcspsync, 4))
   - len = write(fd, &bcsp_sync_resp_pkt, 10);
   + len = dbg_write(fd, &bcsp_sync_resp_pkt, 10);
     else if (!memcmp(bcspp, bcspconf, 4))
   - len = write(fd, &bcsp_conf_resp_pkt, 10);
   + len = dbg_write(fd, &bcsp_conf_resp_pkt, 10);
     else if (!memcmp(bcspp, bcspconfresp,  4))
     break;
     else
   @@ -508,7 +532,7 @@ static int csr(int fd, struct uart_t *u, struct
   termios *ti)

     /* Send command */
     do {
   - if (write(fd, cmd, clen) != clen) {
   + if (dbg_write(fd, cmd, clen) != clen) {
     perror("Failed to write init command (GET_BUILD_ID)");
     return -1;
     }
   @@ -552,7 +576,7 @@ static int csr(int fd, struct uart_t *u, struct
   termios *ti)
    #ifdef CSR_DEBUG
     /* Send command */
     do {
   - if (write(fd, cmd, clen) != clen) {
   + if (dbg_write(fd, cmd, clen) != clen) {
     perror("Failed to write init command (GET_BUILD_ID)");
     return -1;
     }
   @@ -618,7 +642,7 @@ static int csr(int fd, struct uart_t *u, struct
   termios *ti)
    #endif

     /* Send the command to set the CSR UART speed */
   - if (write(fd, cmd, clen) != clen) {
   + if (dbg_write(fd, cmd, clen) != clen) {
     perror("Failed to write init command (SET_UART_SPEED)");
     return -1;
     }
   @@ -673,7 +697,7 @@ static int swave(int fd, struct uart_t *u, struct
   termios *ti)
     }

     /* Send initialization command */
   - if (write(fd, cmd, 10) != 10) {
   + if (dbg_write(fd, cmd, 10) != 10) {
     perror("Failed to write init command");
     return -1;
     }
   @@ -685,7 +709,7 @@ static int swave(int fd, struct uart_t *u, struct
   termios *ti)

     nanosleep(&tm, NULL);

   - r = read(fd, rsp, sizeof(rsp));
   + r = dbg_read(fd, rsp, sizeof(rsp));
     if (r > 0) {
     // guess it's okay, but we should parse the reply. But since
     // I don't react on an error anyway ... todo
   @@ -714,7 +738,7 @@ static int swave(int fd, struct uart_t *u, struct
   termios *ti)
     cmd[3] = 0x00;

     /* Send reset command */
   - if (write(fd, cmd, 4) != 4) {
   + if (dbg_write(fd, cmd, 4) != 4) {
     perror("Can't write Silicon Wave reset cmd.");
     return -1;
     }
   @@ -779,7 +803,7 @@ static int st(int fd, struct uart_t *u, struct
   termios *ti)
     }

     /* Send initialization command */
   - if (write(fd, cmd, 5) != 5) {
   + if (dbg_write(fd, cmd, 5) != 5) {
     perror("Failed to write init command");
     return -1;
     }
   @@ -855,7 +879,7 @@ static int bcm2035(int fd, struct uart_t *u, struct
   termios *ti)
     cmd[3] = 0x00;

     /* Send command */
   - if (write(fd, cmd, 4) != 4) {
   + if (dbg_write(fd, cmd, 4) != 4) {
     fprintf(stderr, "Failed to write reset command\n");
     return -1;
     }
   @@ -877,7 +901,7 @@ static int bcm2035(int fd, struct uart_t *u, struct
   termios *ti)
     str2ba(u->bdaddr, (bdaddr_t *) (cmd + 4));

     /* Send command */
   - if (write(fd, cmd, 10) != 10) {
   + if (dbg_write(fd, cmd, 10) != 10) {
     fprintf(stderr, "Failed to write BD_ADDR command\n");
     return -1;
     }
   @@ -898,7 +922,7 @@ static int bcm2035(int fd, struct uart_t *u, struct
   termios *ti)
     cmd[3] = 0x00;

     /* Send command */
   - if (write(fd, cmd, 4) != 4) {
   + if (dbg_write(fd, cmd, 4) != 4) {
     fprintf(stderr, "Failed to write \"read local version\" "
     "command\n");
     return -1;
   @@ -919,7 +943,7 @@ static int bcm2035(int fd, struct uart_t *u, struct
   termios *ti)
     cmd[3] = 0x00;

     /* Send command */
   - if (write(fd, cmd, 4) != 4) {
   + if (dbg_write(fd, cmd, 4) != 4) {
     fprintf(stderr, "Failed to write \"read local supported "
     "commands\" command\n");
     return -1;
   @@ -965,7 +989,7 @@ static int bcm2035(int fd, struct uart_t *u, struct
   termios *ti)
     cmd[4], cmd[5]);

     /* Send command */
   - if (write(fd, cmd, 6) != 6) {
   + if (dbg_write(fd, cmd, 6) != 6) {
     fprintf(stderr, "Failed to write \"set baud rate\" command\n");
     return -1;
     }