From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43106) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bHyiG-00063G-V8 for qemu-devel@nongnu.org; Tue, 28 Jun 2016 15:30:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bHyiD-00031S-Oh for qemu-devel@nongnu.org; Tue, 28 Jun 2016 15:30:24 -0400 Received: from mail-pf0-x241.google.com ([2607:f8b0:400e:c00::241]:34303) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bHyiD-00031G-DP for qemu-devel@nongnu.org; Tue, 28 Jun 2016 15:30:21 -0400 Received: by mail-pf0-x241.google.com with SMTP id 66so2471698pfy.1 for ; Tue, 28 Jun 2016 12:30:21 -0700 (PDT) Sender: Corey Minyard From: minyard@acm.org Date: Tue, 28 Jun 2016 14:30:12 -0500 Message-Id: <1467142212-29810-1-git-send-email-minyard@acm.org> Subject: [Qemu-devel] [PATCH v2] i2c: Fix SMBus read transactions to avoid double events List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, minyard@acm.org, cminyard@mvista.com Cc: KONRAD Frederic , Alistair Francis , Peter Crosthwaite , Kwon , Peter Maydell From: Corey Minyard Change 2293c27faddf (i2c: implement broadcast write) added broadcast capability to the I2C bus, but it broke SMBus read transactions. An SMBus read transaction does two i2c_start_transaction() calls without an intervening i2c_end_transfer() call. This will result in i2c_start_transfer() adding the same device to the current_devs list twice, and then the ->event() for the same device gets called twice in the second call to i2c_start_transfer(), resulting in the smbus code getting confused. Note that this happens even with pure I2C devices when simulating SMBus over I2C. This fix only scans the bus if the current set of devices is empty. This means that the current set of devices stays fixed until i2c_end_transfer() is called, which is really what you want. This also deletes the empty check from the top of i2c_end_transfer(). It's unnecessary, and it prevents the broadcast variable from being set to false at the end of the transaction if no devices were on the bus. Cc: KONRAD Frederic Cc: Alistair Francis Cc: Peter Crosthwaite Cc: Kwon Cc: Peter Maydell Signed-off-by: Corey Minyard --- hw/i2c/core.c | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) This fix should work with I2C devices as well as SMBus devices. Sorry for not thinking it through all the way before. diff --git a/hw/i2c/core.c b/hw/i2c/core.c index abb3efb..6313d31 100644 --- a/hw/i2c/core.c +++ b/hw/i2c/core.c @@ -101,15 +101,21 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, int recv) bus->broadcast = true; } - QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) { - DeviceState *qdev = kid->child; - I2CSlave *candidate = I2C_SLAVE(qdev); - if ((candidate->address == address) || (bus->broadcast)) { - node = g_malloc(sizeof(struct I2CNode)); - node->elt = candidate; - QLIST_INSERT_HEAD(&bus->current_devs, node, next); - if (!bus->broadcast) { - break; + /* + * If there are already devices in the list, that means we are in + * the middle of a transaction and we shouldn't rescan the bus. + */ + if (QLIST_EMPTY(&bus->current_devs)) { + QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) { + DeviceState *qdev = kid->child; + I2CSlave *candidate = I2C_SLAVE(qdev); + if ((candidate->address == address) || (bus->broadcast)) { + node = g_malloc(sizeof(struct I2CNode)); + node->elt = candidate; + QLIST_INSERT_HEAD(&bus->current_devs, node, next); + if (!bus->broadcast) { + break; + } } } } @@ -134,10 +140,6 @@ void i2c_end_transfer(I2CBus *bus) I2CSlaveClass *sc; I2CNode *node, *next; - if (QLIST_EMPTY(&bus->current_devs)) { - return; - } - QLIST_FOREACH_SAFE(node, &bus->current_devs, next, next) { sc = I2C_SLAVE_GET_CLASS(node->elt); if (sc->event) { -- 2.7.4