Re: [PATCH] serial: imx: fix dcd interrupt firing during probe
From: Stefan Agner <stefan@agner.ch>
Date: 2016-01-25 17:52:54
Also in:
linux-arm-kernel, lkml
Hi Marcel, [also added Lucas] On 2015-12-30 19:12, Marcel Ziswiler wrote:
Continuing on the Apalis iMX6 mainlining work started by Petr Štetiar I noticed that it only boots when rebooting from NXP's downstream 3.14.28 kernel or mainline otherwise (e.g. when cold booted) I did not get any serial debug output at all. Enabling earlyprintk I got the following: [ 1.136806] INFO: trying to register non-static key. [ 1.136871] 2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 25, base_baud = 5000000) is a IMX [ 1.150651] the code is fine but needs lockdep annotation. [ 1.150653] turning off the locking correctness validator. [ 1.150664] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-rc6- next-20151223-00002-g6008f30-dirty #27 [ 1.150668] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) [ 1.150675] Backtrace: [ 1.150701] [<c010c45c>] (dump_backtrace) from [<c010c654>] (show_stack+0x18/0x1c) [ 1.150722] r7:00000000 r6:c0d20848 r5:00000000 r4:00000000 [ 1.150739] [<c010c63c>] (show_stack) from [<c03dadcc>] (dump_stack+0x8c/0xa4) [ 1.150760] [<c03dad40>] (dump_stack) from [<c016b60c>] (__lock_acquire+0x1d88/0x1eb4) [ 1.150774] r7:00000000 r6:c0d063f8 r5:c155f834 r4:e503bc20 [ 1.150785] [<c0169884>] (__lock_acquire) from [<c016bf54>] (lock_acquire+0x74/0x94) [ 1.150803] r10:c0d6eb5e r9:e597b300 r8:00000019 r7:00000001 r6:00000001 r5:60000193 [ 1.150808] r4:00000000 [ 1.150821] [<c016bee0>] (lock_acquire) from [<c08d49d4>] (_raw_spin_lock_irqsave+0x40/0x54) [ 1.150834] r7:000052c8 r6:c0481470 r5:40000193 r4:e503bc10 [ 1.150852] [<c08d4994>] (_raw_spin_lock_irqsave) from [<c0481470>] (imx_rxint+0x20/0x2a4) [ 1.150862] r6:00000000 r5:000052d0 r4:e503bc10 [ 1.150874] [<c0481450>] (imx_rxint) from [<c0482540>] (imx_int+0x170/0x1f4) Debugging a little further I noticed this actually happening after calling devm_request_irq() during serial_imx_probe() even before uart_add_one_port() did initialise the spin_lock acquired in imx_rxint(). Turns out the data carrier detect interrupt fired immediately upon requesting interrupts. This patch fixes this by explicitly disabling data carrier detect before requesting interrupts.
I actually hit a very similar issue on the Colibri iMX6 and hence looked into this too. In our downstream tree, I fixed it in imx_startup, which is probably the wrong place actually...
quoted hunk ↗ jump to hunk
Signed-off-by: Marcel Ziswiler <redacted> --- drivers/tty/serial/imx.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 9362f54c..b1588f9 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c@@ -2032,6 +2032,11 @@ static int serial_imx_probe(struct platform_device *pdev) UCR1_TXMPTYEN | UCR1_RTSDEN); writel_relaxed(reg, sport->port.membase + UCR1); + /* Disable data carrier detect before requesting interrupts */ + reg = readl_relaxed(sport->port.membase + UCR3); + reg &= ~(UCR3_DCD); + writel_relaxed(reg, sport->port.membase + UCR3); +
Note that UCR3_DCD has a different meaning in DCE mode. As a DCE, the bit should be kept 1 (we assume that the carrier is detected by default...) The dte_mode bit should be initialized at that point, hence just making that code conditional should account for that. What I also noticed is that the RI signal suffers the very same issue. We do not use the signal on our Colibri board, but we should disable that interrupt too.