On Sat, Jan 10, 2015 at 01:08:59AM +0100, Stefan Agner wrote: > When the UART is in DMA receive mode (RDMAS set) and one character > just arrived while another interrupt is handled (e.g. TX), the RDRF > (receiver data register full flag) is set due to the water level of > 1. But since the DMA will take care of this character, there is no > need to handle it by calling lpuart_prepare_rx. Handling it leads to > adding the RX timeout timer twice: > > [ 74.336698] Kernel BUG at 80053070 [verbose debug info unavailable] > [ 74.342999] Internal error: Oops - BUG: 0 [#1] ARM0:00.00 khungtaskd > [ 74.347817] Modules linked in: 0 S 0.0 0.0 0:00.00 writeback > [ 74.350926] CPU: 0 PID: 0 Comm: swapper Not tainted 3.19.0-rc3-00001-g39d78e2 #1788 > [ 74.358617] Hardware name: Freescale Vybrid VF610 (Device Tree)t > [ 74.364563] task: 807a7678 ti: 8079c000 task.ti: 8079c000 kblockd > [ 74.370002] PC is at add_timer+0x24/0x28.0 0.0 0:00.09 kworker/u2:1 > [ 74.373960] LR is at lpuart_int+0x15c/0x3d8 > [ 74.378171] pc : [<80053070>] lr : [<802e0d88>] psr: a0010193 > [ 74.378171] sp : 8079de10 ip : 8079de20 fp : 8079de1c > [ 74.389694] r10: 807d44c0 r9 : 8688c300 r8 : 00000013 > [ 74.394943] r7 : 20010193 r6 : 00000000 r5 : 000000a0 r4 : 86997210 > [ 74.401498] r3 : ffffa7da r2 : 80817868 r1 : 86997210 r0 : 86997344 > [ 74.408052] Flags: NzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel > [ 74.415489] Control: 10c5387d Table: 8611c059 DAC: 00000015 > [ 74.421265] Process swapper (pid: 0, stack limit = 0x8079c230) > ... > > Solve this by only execute the receiver path (lpuart_prepare_rx) if > the DMA receive mode (RDMAS) is not set. Also, make sure the flag is > cleared on initialization, in case it has been left set. > > This can be best reproduced using UART as a serial console, then > running top while dd'ing data into the terminal. > > Signed-off-by: Stefan Agner <stefan@xxxxxxxx> > --- > drivers/tty/serial/fsl_lpuart.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) Same stable question as before. -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
