From d3c4c1f29aadccf2f43530bfa1e60a6d8030fd4a Mon Sep 17 00:00:00 2001 From: Dave Penkler Date: Sun, 28 Sep 2025 11:18:18 +0200 Subject: [PATCH] staging: gpib: Fix no EOI on 1 and 2 byte writes EOI (End Or Identify) is a hardware line on the GPIB bus that can be asserted with the last byte of a message to indicate the end of the transfer to the receiving device. In this driver, a write with send_eoi true is done in 3 parts: Send first byte directly Send remaining but 1 bytes using the fifo Send the last byte directly with EOI asserted The first byte in a write is always sent by writing to the tms9914 chip directly to setup for the subsequent fifo transfer. We were not checking for a 1 byte write with send_eoi true resulting in EOI not being asserted. Since the fifo transfer was not executed (fifotransfersize == 0) the retval in the test after the fifo transfer code was still 1 from the preceding direct write. This caused it to return without executing the final direct write which would have sent an unsollicited extra byte. For a 2 byte message the first byte was sent directly. But since the fifo transfer was not executed (fifotransfersize == 1) and the retval in the test after the fifo transfer code was still 1 from the preceding first byte write it returned before the final direct byte write with send_eoi true. The second byte was then sent as a separate 1 byte write to complete the 2 byte write count again without EOI being asserted as above. Only send the first byte directly if more than 1 byte is to be transferred with send_eoi true. Also check for retval < 0 for the error return in case the fifo code is not used (1 or 2 byte message with send_eoi true). Fixes: 09a4655ee1eb ("staging: gpib: Add HP/Agilent/Keysight 8235xx PCI GPIB driver") Cc: stable Tested-by: Dave Penkler Signed-off-by: Dave Penkler Signed-off-by: Greg Kroah-Hartman --- drivers/staging/gpib/agilent_82350b/agilent_82350b.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/staging/gpib/agilent_82350b/agilent_82350b.c b/drivers/staging/gpib/agilent_82350b/agilent_82350b.c index 94bbb3b6576d..01a5bb43cd2d 100644 --- a/drivers/staging/gpib/agilent_82350b/agilent_82350b.c +++ b/drivers/staging/gpib/agilent_82350b/agilent_82350b.c @@ -182,10 +182,12 @@ static int agilent_82350b_accel_write(struct gpib_board *board, u8 *buffer, return retval; #endif - retval = agilent_82350b_write(board, buffer, 1, 0, &num_bytes); - *bytes_written += num_bytes; - if (retval < 0) - return retval; + if (fifotransferlength > 0) { + retval = agilent_82350b_write(board, buffer, 1, 0, &num_bytes); + *bytes_written += num_bytes; + if (retval < 0) + return retval; + } write_byte(tms_priv, tms_priv->imr0_bits & ~HR_BOIE, IMR0); for (i = 1; i < fifotransferlength;) { @@ -217,7 +219,7 @@ static int agilent_82350b_accel_write(struct gpib_board *board, u8 *buffer, break; } write_byte(tms_priv, tms_priv->imr0_bits, IMR0); - if (retval) + if (retval < 0) return retval; if (send_eoi) { -- 2.47.3