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Subject[PATCH 4.9 132/165] tty: serial: imx: setup the correct sg entry for tx dma
Date
From: Fugang Duan <fugang.duan@nxp.com>

commit f76707831829530ffdd3888bebc108aecefccaa0 upstream.

There has oops as below happen on i.MX8MP EVK platform that has
6G bytes DDR memory.

when (xmit->tail < xmit->head) && (xmit->head == 0),
it setups one sg entry with sg->length is zero:
sg_set_buf(sgl + 1, xmit->buf, xmit->head);

if xmit->buf is allocated from >4G address space, and SDMA only
support <4G address space, then dma_map_sg() will call swiotlb_map()
to do bounce buffer copying and mapping.

But swiotlb_map() don't allow sg entry's length is zero, otherwise
report BUG_ON().

So the patch is to correct the tx DMA scatter list.

Oops:
[ 287.675715] kernel BUG at kernel/dma/swiotlb.c:497!
[ 287.680592] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[ 287.686075] Modules linked in:
[ 287.689133] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.4.3-00016-g3fdc4e0-dirty #10
[ 287.696872] Hardware name: FSL i.MX8MP EVK (DT)
[ 287.701402] pstate: 80000085 (Nzcv daIf -PAN -UAO)
[ 287.706199] pc : swiotlb_tbl_map_single+0x1fc/0x310
[ 287.711076] lr : swiotlb_map+0x60/0x148
[ 287.714909] sp : ffff800010003c00
[ 287.718221] x29: ffff800010003c00 x28: 0000000000000000
[ 287.723533] x27: 0000000000000040 x26: ffff800011ae0000
[ 287.728844] x25: ffff800011ae09f8 x24: 0000000000000000
[ 287.734155] x23: 00000001b7af9000 x22: 0000000000000000
[ 287.739465] x21: ffff000176409c10 x20: 00000000001f7ffe
[ 287.744776] x19: ffff000176409c10 x18: 000000000000002e
[ 287.750087] x17: 0000000000000000 x16: 0000000000000000
[ 287.755397] x15: 0000000000000000 x14: 0000000000000000
[ 287.760707] x13: ffff00017f334000 x12: 0000000000000001
[ 287.766018] x11: 00000000001fffff x10: 0000000000000000
[ 287.771328] x9 : 0000000000000003 x8 : 0000000000000000
[ 287.776638] x7 : 0000000000000000 x6 : 0000000000000000
[ 287.781949] x5 : 0000000000200000 x4 : 0000000000000000
[ 287.787259] x3 : 0000000000000001 x2 : 00000001b7af9000
[ 287.792570] x1 : 00000000fbfff000 x0 : 0000000000000000
[ 287.797881] Call trace:
[ 287.800328] swiotlb_tbl_map_single+0x1fc/0x310
[ 287.804859] swiotlb_map+0x60/0x148
[ 287.808347] dma_direct_map_page+0xf0/0x130
[ 287.812530] dma_direct_map_sg+0x78/0xe0
[ 287.816453] imx_uart_dma_tx+0x134/0x2f8
[ 287.820374] imx_uart_dma_tx_callback+0xd8/0x168
[ 287.824992] vchan_complete+0x194/0x200
[ 287.828828] tasklet_action_common.isra.0+0x154/0x1a0
[ 287.833879] tasklet_action+0x24/0x30
[ 287.837540] __do_softirq+0x120/0x23c
[ 287.841202] irq_exit+0xb8/0xd8
[ 287.844343] __handle_domain_irq+0x64/0xb8
[ 287.848438] gic_handle_irq+0x5c/0x148
[ 287.852185] el1_irq+0xb8/0x180
[ 287.855327] cpuidle_enter_state+0x84/0x360
[ 287.859508] cpuidle_enter+0x34/0x48
[ 287.863083] call_cpuidle+0x18/0x38
[ 287.866571] do_idle+0x1e0/0x280
[ 287.869798] cpu_startup_entry+0x20/0x40
[ 287.873721] rest_init+0xd4/0xe0
[ 287.876949] arch_call_rest_init+0xc/0x14
[ 287.880958] start_kernel+0x420/0x44c
[ 287.884622] Code: 9124c021 9417aff8 a94363f7 17ffffd5 (d4210000)
[ 287.890718] ---[ end trace 5bc44c4ab6b009ce ]---
[ 287.895334] Kernel panic - not syncing: Fatal exception in interrupt
[ 287.901686] SMP: stopping secondary CPUs
[ 288.905607] SMP: failed to stop secondary CPUs 0-1
[ 288.910395] Kernel Offset: disabled
[ 288.913882] CPU features: 0x0002,2000200c
[ 288.917888] Memory Limit: none
[ 288.920944] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

Reported-by: Eagle Zhou <eagle.zhou@nxp.com>
Tested-by: Eagle Zhou <eagle.zhou@nxp.com>
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Cc: stable <stable@vger.kernel.org>
Fixes: 7942f8577f2a ("serial: imx: TX DMA: clean up sg initialization")
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/1581401761-6378-1-git-send-email-fugang.duan@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/tty/serial/imx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -532,7 +532,7 @@ static void imx_dma_tx(struct imx_port *

sport->tx_bytes = uart_circ_chars_pending(xmit);

- if (xmit->tail < xmit->head) {
+ if (xmit->tail < xmit->head || xmit->head == 0) {
sport->dma_tx_nents = 1;
sg_init_one(sgl, xmit->buf + xmit->tail, sport->tx_bytes);
} else {

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