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[PATCH 4.4 42/45] tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done

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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Genoud <richard.genoud@gmail.com>

commit b389f173aaa1204d6dc1f299082a162eb0491545 upstream.

When using RS485 in half duplex, RX should be enabled when TX is
finished, and stopped when TX starts.

Before commit 0058f0871efe7b01c6 ("tty/serial: atmel: fix RS485 half
duplex with DMA"), RX was not disabled in atmel_start_tx() if the DMA
was used. So, collisions could happened.

But disabling RX in atmel_start_tx() uncovered another bug:
RX was enabled again in the wrong place (in atmel_tx_dma) instead of
being enabled when TX is finished (in atmel_complete_tx_dma), so the
transmission simply stopped.

This bug was not triggered before commit 0058f0871efe7b01c6
("tty/serial: atmel: fix RS485 half duplex with DMA") because RX was
never disabled before.

Moving atmel_start_rx() in atmel_complete_tx_dma() corrects the problem.

Reported-by: Gil Weber <webergil@gmail.com>
Fixes: 0058f0871efe7b01c6
Tested-by: Gil Weber <webergil@gmail.com>
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Tested-by: Bryan Evenson <bevenson@melinkcorp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/serial/atmel_serial.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -810,6 +810,11 @@ static void atmel_complete_tx_dma(void *
 	 */
 	if (!uart_circ_empty(xmit))
 		tasklet_schedule(&atmel_port->tasklet);
+	else if ((port->rs485.flags & SER_RS485_ENABLED) &&
+		 !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
+		/* DMA done, stop TX, start RX for RS485 */
+		atmel_start_rx(port);
+	}
 
 	spin_unlock_irqrestore(&port->lock, flags);
 }
@@ -912,12 +917,6 @@ static void atmel_tx_dma(struct uart_por
 		desc->callback = atmel_complete_tx_dma;
 		desc->callback_param = atmel_port;
 		atmel_port->cookie_tx = dmaengine_submit(desc);
-
-	} else {
-		if (port->rs485.flags & SER_RS485_ENABLED) {
-			/* DMA done, stop TX, start RX for RS485 */
-			atmel_start_rx(port);
-		}
 	}
 
 	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)

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[PATCH 4.4 00/45] 4.4.63-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:00 +0200
  [PATCH 4.4 44/45] sctp: deny peeloff operation on asocs with threads sleeping on it Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:00 +0200
  [PATCH 4.4 32/45] mm: Tighten x86 /dev/mem with zeroing reads Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:00 +0200
  [PATCH 4.4 16/45] xen, fbfront: fix connecting to backend Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 15/45] scsi: sd: Fix capacity calculation with 32-bit sector_t Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 27/45] ath9k: fix NULL pointer dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 20/45] char: Drop bogus dependency of DEVPORT on !M68K Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 11/45] iscsi-target: Fix TMR reference leak during session shutdown Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 23/45] kvm: fix page struct leak in handle_vmon Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 12/45] iscsi-target: Drop work-around for legacy GlobalSAN initiator Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 10/45] acpi, nfit, libnvdimm: fix interleave set cookie calculation (64-bit comparison) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 14/45] scsi: sd: Consider max_xfer_blocks if opt_xfer_blocks is unusable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 03/45] drm/nouveau/mpeg: mthd returns true on success now Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 06/45] Input: xpad - add support for Razer Wildcat gamepad Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 39/45] catc: Use heap buffer for memory size test Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 25/45] powerpc: Disable HFSCR[TM] if TM is not supported Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 07/45] perf/x86: Avoid exposing wrong/stale data in intel_pmu_lbr_read_32() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 41/45] SUNRPC: fix refcounting problems with auth_gss messages. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 02/45] thp: fix MADV_DONTNEED vs clear soft dirty race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 31/45] rtc: tegra: Implement clock handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 17/45] libnvdimm: fix reconfig_mutex, mmap_sem, and jbd2_handle lockdep splat Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 05/45] CIFS: store results of cifs_reopen_file to avoid infinite wait Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 08/45] x86/vdso: Ensure vdso32_enabled gets set to valid values only Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 40/45] ibmveth: calculate gso_segs for large packets Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 21/45] char: lack of bool string made CONFIG_DEVPORT always on Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 42/45] tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 38/45] catc: Combine failure cleanup code in catc_probe() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 26/45] crypto: ahash - Fix EINPROGRESS notification callback Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  [PATCH 4.4 01/45] cgroup, kthread: close race window where new kthreads can be migrated to non-root cgroups Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-19 17:10 +0200
  Re: [PATCH 4.4 00/45] 4.4.63-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-04-19 22:40 +0200
  Re: [PATCH 4.4 00/45] 4.4.63-stable review Guenter Roeck <linux@roeck-us.net> - 2017-04-20 01:30 +0200

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