From: Peter Maydell <[email protected]> The documentation of the Xilinx DisplayPort subsystem at https://www.xilinx.com/support/documents/ip_documentation/v_dp_txss1/v3_1/pg299-v-dp-txss1.pdf doesn't say what happens if a guest tries to issue an AUX write command with a length greater than the amount of data in the AUX write FIFO, or tries to write more data to the write FIFO than it can hold, or issues multiple commands that put data into the AUX read FIFO without reading it such that it overflows.
Currently QEMU will abort() in these guest-error situations, either in xlnx_dp.c itself or in the fifo8 code. Make these cases all be logged as guest errors instead. We choose to ignore the new data on overflow, and return 0 on underflow. This is in line with how we handled the "read from empty RX FIFO" case in commit a09ef5040477. Cc: [email protected] Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1418 Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1419 Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1424 Signed-off-by: Peter Maydell <[email protected]> Reviewed-by: Philippe Mathieu-Daudé <[email protected]> Reviewed-by: Edgar E. Iglesias <[email protected]> Message-id: [email protected] (cherry picked from commit f52db7f34242d3398bab0bacaa3e5dde99be5258) Signed-off-by: Michael Tokarev <[email protected]> diff --git a/hw/display/xlnx_dp.c b/hw/display/xlnx_dp.c index 7c980ee642..4120f03a3b 100644 --- a/hw/display/xlnx_dp.c +++ b/hw/display/xlnx_dp.c @@ -435,7 +435,18 @@ static void xlnx_dp_aux_clear_rx_fifo(XlnxDPState *s) static void xlnx_dp_aux_push_rx_fifo(XlnxDPState *s, uint8_t *buf, size_t len) { + size_t avail = fifo8_num_free(&s->rx_fifo); DPRINTF("Push %u data in rx_fifo\n", (unsigned)len); + if (len > avail) { + /* + * Data sheet doesn't specify behaviour here: we choose to ignore + * the excess data. + */ + qemu_log_mask(LOG_GUEST_ERROR, + "%s: ignoring %zu bytes pushed to full RX_FIFO\n", + __func__, len - avail); + len = avail; + } fifo8_push_all(&s->rx_fifo, buf, len); } @@ -466,7 +477,18 @@ static void xlnx_dp_aux_clear_tx_fifo(XlnxDPState *s) static void xlnx_dp_aux_push_tx_fifo(XlnxDPState *s, uint8_t *buf, size_t len) { + size_t avail = fifo8_num_free(&s->tx_fifo); DPRINTF("Push %u data in tx_fifo\n", (unsigned)len); + if (len > avail) { + /* + * Data sheet doesn't specify behaviour here: we choose to ignore + * the excess data. + */ + qemu_log_mask(LOG_GUEST_ERROR, + "%s: ignoring %zu bytes pushed to full TX_FIFO\n", + __func__, len - avail); + len = avail; + } fifo8_push_all(&s->tx_fifo, buf, len); } @@ -475,8 +497,10 @@ static uint8_t xlnx_dp_aux_pop_tx_fifo(XlnxDPState *s) uint8_t ret; if (fifo8_is_empty(&s->tx_fifo)) { - error_report("%s: TX_FIFO underflow", __func__); - abort(); + /* Data sheet doesn't specify behaviour here: we choose to return 0 */ + qemu_log_mask(LOG_GUEST_ERROR, "%s: attempt to read empty TX_FIFO\n", + __func__); + return 0; } ret = fifo8_pop(&s->tx_fifo); DPRINTF("pop 0x%2.2X from tx_fifo.\n", ret); -- 2.47.3
