From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54019) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fHF6r-0002AS-HJ for qemu-devel@nongnu.org; Fri, 11 May 2018 16:57:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fHF6q-000547-FW for qemu-devel@nongnu.org; Fri, 11 May 2018 16:57:49 -0400 Received: from mail-io0-x244.google.com ([2607:f8b0:4001:c06::244]:33900) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1fHF6q-00053z-BI for qemu-devel@nongnu.org; Fri, 11 May 2018 16:57:48 -0400 Received: by mail-io0-x244.google.com with SMTP id p124-v6so8516445iod.1 for ; Fri, 11 May 2018 13:57:48 -0700 (PDT) From: Calvin Lee Date: Fri, 11 May 2018 14:57:23 -0600 Message-Id: <20180511205724.4039-2-cyrus296@gmail.com> In-Reply-To: <20180511205724.4039-1-cyrus296@gmail.com> References: <20180511205724.4039-1-cyrus296@gmail.com> Subject: [Qemu-devel] [PATCH RFC 1/2] PC Chipset: Improve serial divisor calculation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: mst@redhat.com, pbonzini@redhat.com, dgilbert@redhat.com, Calvin Lee This fixes several problems I found in the UART serial implementation. Now all divisor values are allowed, while before divisor values of zero and below the base baud rate were rejected. All changes are in reference to http://www.sci.muni.cz/docs/pc/serport.txt Signed-off-by: Calvin Lee --- I included a slight code-style change in this commit because it seemed close enough to the code I was editing to be relevant. If not, I can change the commit to not include this change. hw/char/serial.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/hw/char/serial.c b/hw/char/serial.c index 2c080c9862..4159a46a2f 100644 --- a/hw/char/serial.c +++ b/hw/char/serial.c @@ -150,13 +150,10 @@ static void serial_update_irq(SerialState *s) static void serial_update_parameters(SerialState *s) { - int speed, parity, data_bits, stop_bits, frame_size; + float speed; + int parity, data_bits, stop_bits, frame_size; QEMUSerialSetParams ssp; - if (s->divider == 0 || s->divider > s->baudbase) { - return; - } - /* Start bit. */ frame_size = 1; if (s->lcr & 0x08) { @@ -169,14 +166,16 @@ static void serial_update_parameters(SerialState *s) } else { parity = 'N'; } - if (s->lcr & 0x04) + if (s->lcr & 0x04) { stop_bits = 2; - else + } else { stop_bits = 1; + } data_bits = (s->lcr & 0x03) + 5; frame_size += data_bits + stop_bits; - speed = s->baudbase / s->divider; + /* Zero divisor should give about 3500 baud */ + speed = (s->divider == 0) ? 3500 : (float) s->baudbase / s->divider; ssp.speed = speed; ssp.parity = parity; ssp.data_bits = data_bits; @@ -184,7 +183,7 @@ static void serial_update_parameters(SerialState *s) s->char_transmit_time = (NANOSECONDS_PER_SECOND / speed) * frame_size; qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp); - DPRINTF("speed=%d parity=%c data=%d stop=%d\n", + DPRINTF("speed=%.2f parity=%c data=%d stop=%d\n", speed, parity, data_bits, stop_bits); } @@ -341,7 +340,11 @@ static void serial_ioport_write(void *opaque, hwaddr addr, uint64_t val, default: case 0: if (s->lcr & UART_LCR_DLAB) { - s->divider = (s->divider & 0xff00) | val; + if (size == 2) { + s->divider = (s->divider & 0xff00) | val; + } else if (size == 4) { + s->divider = val; + } serial_update_parameters(s); } else { s->thr = (uint8_t) val; -- 2.17.0