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stmmac: fix potential division by 0
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When the MAC is connected to a 10 Mb/s PHY and the PTP clock is derived
from the MAC reference clock (default), the clk_ptp_rate becomes too
small and the calculated sub second increment becomes 0 when computed by
the stmmac_config_sub_second_increment() function within
stmmac_init_tstamp_counter().

Therefore, the subsequent div_u64 in stmmac_init_tstamp_counter()
operation triggers a divide by 0 exception as shown below.

[   95.062067] socfpga-dwmac ff700000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
[   95.076440] socfpga-dwmac ff700000.ethernet eth0: PHY [stmmac-0:08] driver [NCN26000] (irq=49)
[   95.095964] dwmac1000: Master AXI performs any burst length
[   95.101588] socfpga-dwmac ff700000.ethernet eth0: No Safety Features support found
[   95.109428] Division by zero in kernel.
[   95.113447] CPU: 0 PID: 239 Comm: ifconfig Not tainted 6.1.0-rc7-centurion3-1.0.3.0-01574-gb624218205b7-dirty #77
[   95.123686] Hardware name: Altera SOCFPGA
[   95.127695]  unwind_backtrace from show_stack+0x10/0x14
[   95.132938]  show_stack from dump_stack_lvl+0x40/0x4c
[   95.137992]  dump_stack_lvl from Ldiv0+0x8/0x10
[   95.142527]  Ldiv0 from __aeabi_uidivmod+0x8/0x18
[   95.147232]  __aeabi_uidivmod from div_u64_rem+0x1c/0x40
[   95.152552]  div_u64_rem from stmmac_init_tstamp_counter+0xd0/0x164
[   95.158826]  stmmac_init_tstamp_counter from stmmac_hw_setup+0x430/0xf00
[   95.165533]  stmmac_hw_setup from __stmmac_open+0x214/0x2d4
[   95.171117]  __stmmac_open from stmmac_open+0x30/0x44
[   95.176182]  stmmac_open from __dev_open+0x11c/0x134
[   95.181172]  __dev_open from __dev_change_flags+0x168/0x17c
[   95.186750]  __dev_change_flags from dev_change_flags+0x14/0x50
[   95.192662]  dev_change_flags from devinet_ioctl+0x2b4/0x604
[   95.198321]  devinet_ioctl from inet_ioctl+0x1ec/0x214
[   95.203462]  inet_ioctl from sock_ioctl+0x14c/0x3c4
[   95.208354]  sock_ioctl from vfs_ioctl+0x20/0x38
[   95.212984]  vfs_ioctl from sys_ioctl+0x250/0x844
[   95.217691]  sys_ioctl from ret_fast_syscall+0x0/0x4c
[   95.222743] Exception stack(0xd0ee1fa8 to 0xd0ee1ff0)
[   95.227790] 1fa0:                   00574c4f be9aeca4 00000003 00008914 be9aeca4 be9aec50
[   95.235945] 1fc0: 00574c4f be9aeca4 0059f078 00000036 be9aee8c be9aef7a 00000015 00000000
[   95.244096] 1fe0: 005a01f0 be9aec38 004d7484 b6e67d74

Signed-off-by: Piergiorgio Beruto <[email protected]>
Fixes: 91a2559 ("net: stmmac: Fix sub-second increment")
Reviewed-by: Andrew Lunn <[email protected]>
Link: https://lore.kernel.org/r/de4c64ccac9084952c56a06a8171d738604c4770.1670678513.git.piergiorgio.beruto@gmail.com
Signed-off-by: Jakub Kicinski <[email protected]>
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@pberuto @kuba-moo
pberuto authored and kuba-moo committed Dec 12, 2022
1 parent 87c9781 commit ede5a38
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Showing 2 changed files with 3 additions and 2 deletions.
3 changes: 2 additions & 1 deletion drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,8 @@ static void config_sub_second_increment(void __iomem *ioaddr,
if (!(value & PTP_TCR_TSCTRLSSR))
data = (data * 1000) / 465;

data &= PTP_SSIR_SSINC_MASK;
if (data > PTP_SSIR_SSINC_MAX)
data = PTP_SSIR_SSINC_MAX;

reg_value = data;
if (gmac4)
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2 changes: 1 addition & 1 deletion drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,7 @@
#define PTP_TCR_TSENMACADDR BIT(18)

/* SSIR defines */
#define PTP_SSIR_SSINC_MASK 0xff
#define PTP_SSIR_SSINC_MAX 0xff
#define GMAC4_PTP_SSIR_SSINC_SHIFT 16

/* Auxiliary Control defines */
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