Re: serial console on Mikrotik RB532 non-working

[Waldemar Brodkorb <wbx@openadk.org>]

Hi, 

friendly ping.

Nobody has an idea how to fix it without revert?

best regards
 Waldemar

Waldemar Brodkorb wrote,

> Hi Mips people,
> Jonas Gorski wrote,
> 
> > On Wed, Feb 4, 2026 at 12:19 PM Waldemar Brodkorb <wbx@openadk.org> wrote:
> > >
> > > Hi Jonas,
> > > Jonas Gorski wrote,
> > >
> > > > Hi,
> > > >
> > > > On Tue, Feb 3, 2026 at 7:25 PM Waldemar Brodkorb <wbx@openadk.org> wrote:
> > > > >
> > > > > Hi Jiaxun,
> > > > > Jiaxun Yang wrote,
> > > > > >
> > > > > > On Tue, 3 Feb 2026, at 3:24 PM, Jiaxun Yang wrote:
> > > > > > > On Sun, 1 Feb 2026, at 6:39 PM, Waldemar Brodkorb wrote:
> > > > > > >> Hi MIPS hackers,
> > > > > > >>
> > > > > > >> I want to use the latest Linux kernel on my Mikrotik RB532, but the
> > > > > > >> serial console is non working. I bisected the problem and the first
> > > > > > >> breaking change is this commit:
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > Can you try this?
> > > > > >
> > > > > > Oops sorry I missed a flag, it should be:
> > > > > >
> > > > > > diff --git a/arch/mips/rb532/devices.c b/arch/mips/rb532/devices.c
> > > > > > index 8ecb56be81ac..239018540221 100644
> > > > > > --- a/arch/mips/rb532/devices.c
> > > > > > +++ b/arch/mips/rb532/devices.c
> > > > > > @@ -213,11 +213,12 @@ static struct platform_device rb532_wdt = {
> > > > > >  static struct plat_serial8250_port rb532_uart_res[] = {
> > > > > >         {
> > > > > >                 .type           = PORT_16550A,
> > > > > > -               .membase        = (char *)KSEG1ADDR(REGBASE + UART0BASE),
> > > > > > +               .mapbase        = REGBASE + UART0BASE,
> > > > > > +               .mapsize        = SZ_4K,
> > > > > >                 .irq            = UART0_IRQ,
> > > > > >                 .regshift       = 2,
> > > > > >                 .iotype         = UPIO_MEM,
> > > > > > -               .flags          = UPF_BOOT_AUTOCONF,
> > > > > > +               .flags          = UPF_BOOT_AUTOCONF | UPF_IOREMAP,
> > > > > >         },
> > > > > >         {
> > > > > >                 .flags          = 0,
> > > > > >
> > > > >
> > > > > I tried the patch, but it still hangs here:
> > > > >
> > > > > RouterBOOT booter 2.18
> > > > >
> > > > > RouterBoard 532
> > > > >
> > > > > CPU frequency: 399 MHz
> > > > >   Memory size:  32 MB
> > > > >
> > > > > Press any key within 3 seconds to enter setup...
> > > > > trying dhcp protocol... OK
> > > > > resolved mac address 9C:BF:0D:00:D6:4E
> > > > > Gateway: 192.168.1.254
> > > > > transfer started ........................................ transfer ok, time=525.70s
> > > > > setting up elf image... OK
> > > > > jumping to kernel code
> > > > >
> > > > > Nothing in tcpdump tries to mount nfs, so I believe serial console
> > > > > breakage is not the only problem here.
> > > >
> > > > Have you tried the patch on top of master or
> > > > 6e690d54cfa802f939cefbd2fa2c91bd0b8bd1b6?
> > > >
> > > > If it works on top of 6e690d54cfa802f939cefbd2fa2c91bd0b8bd1b6, then
> > > > it fixes the serial issue, and you can do a new git bisect between
> > > > 6e690d54cfa802f939cefbd2fa2c91bd0b8bd1b6 and master to find the next
> > > > breakage, with the patch re-applied on top each step (so serial stays
> > > > working).
> > >
> > > Yes, thanks for the idea. I already had this idea in mind and I am 9
> > > steps before I get the next breakage :)
> > >
> > > Thanks for the heads up,
> > 
> > Also a small warning when doing a bisect with git am'd patches on top:
> > always (git) reset to the original tested commit before doing git
> > bisect <bood|bad>, else git bisect will account for these commits on
> > top in calculating the next revision to test and may suggest the very
> > same commit again you were originally testing.
> > 
> > It took a me a few steps until I noticed I was running in circles when
> > I had to bisect with a few patches on top.
> 
> I just used patch and git stash for the job :)
> So here is the result, the failing commit is:
> commit 9f048fa487409e364cf866c957cf0b0d782ca5a3 (HEAD)
> Author: Maciej W. Rozycki <macro@orcam.me.uk>
> Date:   Thu Nov 13 05:21:10 2025 +0000
> 
>     MIPS: mm: Prevent a TLB shutdown on initial uniquification
> 
>     Depending on the particular CPU implementation a TLB shutdown may occur
>     if multiple matching entries are detected upon the execution of a TLBP
>     or the TLBWI/TLBWR instructions.  Given that we don't know what entries
>     we have been handed we need to be very careful with the initial TLB
>     setup and avoid all these instructions.
> 
>     Therefore read all the TLB entries one by one with the TLBR instruction,
>     bypassing the content addressing logic, and truncate any large pages in
>     place so as to avoid a case in the second step where an incoming entry
>     for a large page at a lower address overlaps with a replacement entry
>     chosen at another index.  Then preinitialize the TLB using addresses
>     outside our usual unique range and avoiding clashes with any entries
>     received, before making the usual call to local_flush_tlb_all().
> 
>     This fixes (at least) R4x00 cores if TLBP hits multiple matching TLB
>     entries (SGI IP22 PROM for examples sets up all TLBs to the same virtual
>     address).
> 
>     Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
>     Fixes: 35ad7e181541 ("MIPS: mm: tlb-r4k: Uniquify TLB entries on init")
>     Cc: stable@vger.kernel.org
>     Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
>     Tested-by: Jiaxun Yang <jiaxun.yang@flygoat.com> # Boston I6400, M5150 sim
>     Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> 
> Reverting this commit, make the RB532 boot. I need the UART patch, too.
> 
> Attached is the dmesg from the device.
> 
> Anyone knows how to fix this issue?
> 
> best regards
>  Waldemar
> 
> 

> [    0.000000] Linux version 6.19.0-rc8+ (wbx@fluor) (mipsel-openadk-linux-uclibc-gcc (GCC) 15.2.0, GNU ld (GNU Binutils) 2.45.1) #50 Wed Feb  4 16:41:19 CET 2026
> [    0.000000] CPU0 revision is: 0001800a (MIPS 4Kc)
> [    0.000000] User-defined physical RAM map overwrite
> [    0.000000] Primary instruction cache 8kB, VIPT, 4-way, linesize 16 bytes.
> [    0.000000] Primary data cache 8kB, 4-way, VIPT, no aliases, linesize 16 bytes
> [    0.000000] Zone ranges:
> [    0.000000]   Normal   [mem 0x0000000000000000-0x0000000001ffffff]
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000000000000-0x0000000001ffffff]
> [    0.000000] Initmem setup node 0 [mem 0x0000000000000000-0x0000000001ffffff]
> [    0.000000] pcpu-alloc: s0 r0 d32768 u32768 alloc=1*32768
> [    0.000000] pcpu-alloc: [0] 0 
> [    0.000000] Kernel command line: console=ttyS0,115200 gpio=16383 mem=32M kmac=00:0C:42:0A:7D:D3 board=500 boot=1   console=ttyS0,115200 rw root=/dev/nfs ip=dhcp nfsroot=192.168.1.254:/srv/nfs/rb532
> [    0.000000] korina mac = 00:0C:42:0A:7D:D3
> [    0.000000] Unknown kernel command line parameters "gpio=16383 board=500 boot=1", will be passed to user space.
> [    0.000000] printk: log buffer data + meta data: 131072 + 409600 = 540672 bytes
> [    0.000000] Dentry cache hash table entries: 4096 (order: 2, 16384 bytes, linear)
> [    0.000000] Inode-cache hash table entries: 2048 (order: 1, 8192 bytes, linear)
> [    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 8192
> [    0.000000] mem auto-init: stack:all(zero), heap alloc:off, heap free:off
> [    0.000000] SLUB: HWalign=16, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> [    0.000000] NR_IRQS: 256
> [    0.000000] Initializing IRQ's: 168 out of 256
> [    0.000000] calculating r4koff... 
> [    0.000000] 000c34f8(799992)
> [    0.000000] CPU frequency 400.00 MHz
> [    0.000000] clocksource: MIPS: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 9556397797 ns
> [    0.000010] sched_clock: 32 bits at 200MHz, resolution 5ns, wraps every 10737525757ns
> [    0.000236] Calibrating delay loop... 397.82 BogoMIPS (lpj=795648)
> [    0.032139] pid_max: default: 32768 minimum: 301
> [    0.033029] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
> [    0.033136] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
> [    0.042812] Memory: 26612K/32768K available (3993K kernel code, 542K rwdata, 548K rodata, 152K init, 188K bss, 5760K reserved, 0K cma-reserved)
> [    0.044819] devtmpfs: initialized
> [    0.053484] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
> [    0.053636] posixtimers hash table entries: 512 (order: 0, 2048 bytes, linear)
> [    0.053740] futex hash table entries: 256 (4096 bytes on 1 NUMA nodes, total 4 KiB, linear).
> [    0.060069] NET: Registered PF_NETLINK/PF_ROUTE protocol family
> [    0.062045] gpio gpiochip0: Static allocation of GPIO base is deprecated, use dynamic allocation.
> [    0.064668] PCI: Initializing PCI
> [    0.070830] SCSI subsystem initialized
> [    0.071977] libata version 3.00 loaded.
> [    0.074816] PCI host bridge to bus 0000:00
> [    0.074882] pci_bus 0000:00: root bus resource [mem 0x50000000-0x5fffffff]
> [    0.074978] pci_bus 0000:00: root bus resource [io  0x18800000-0x188fffff]
> [    0.075066] pci_bus 0000:00: No busn resource found for root bus, will use [bus 00-ff]
> [    0.075217] pci 0000:00:00.0: [111d:0000] type 00 class 0x000000 conventional PCI endpoint
> [    0.075353] pci 0000:00:00.0: BAR 0 [mem 0x00000000-0x07ffffff pref]
> [    0.075449] pci 0000:00:00.0: [Firmware Bug]: BAR 1: invalid; can't size
> [    0.075512] pci 0000:00:00.0: [Firmware Bug]: BAR 2: invalid; can't size
> [    0.101583] pci 0000:00:02.0: [1106:3106] type 00 class 0x020000 conventional PCI endpoint
> [    0.101736] pci 0000:00:02.0: BAR 0 [io  0x0000-0x00ff]
> [    0.101831] pci 0000:00:02.0: BAR 1 [mem 0x00000000-0x000000ff]
> [    0.102022] pci 0000:00:02.0: supports D1 D2
> [    0.102087] pci 0000:00:02.0: PME# supported from D1 D2 D3hot D3cold
> [    0.102883] pci 0000:00:03.0: [1106:3106] type 00 class 0x020000 conventional PCI endpoint
> [    0.103036] pci 0000:00:03.0: BAR 0 [io  0x0000-0x00ff]
> [    0.103131] pci 0000:00:03.0: BAR 1 [mem 0x00000000-0x000000ff]
> [    0.103322] pci 0000:00:03.0: supports D1 D2
> [    0.103386] pci 0000:00:03.0: PME# supported from D1 D2 D3hot D3cold
> [    0.104215] pci 0000:00:04.0: [13a3:0020] type 00 class 0x0b4000 conventional PCI endpoint
> [    0.104368] pci 0000:00:04.0: BAR 0 [mem 0x00000000-0x00000fff]
> [    0.104463] pci 0000:00:04.0: BAR 1 [mem 0x00000000-0x00001fff]
> [    0.104553] pci 0000:00:04.0: BAR 2 [mem 0x00000000-0x00007fff]
> [    0.584389] pci_bus 0000:00: busn_res: [bus 00-ff] end is updated to 00
> [    0.584536] pci 0000:00:04.0: BAR 2 [mem 0x50000000-0x50007fff]: assigned
> [    0.584656] pci 0000:00:04.0: BAR 1 [mem 0x50008000-0x50009fff]: assigned
> [    0.584771] pci 0000:00:04.0: BAR 0 [mem 0x5000a000-0x5000afff]: assigned
> [    0.584887] pci 0000:00:02.0: BAR 0 [io  0x18800000-0x188000ff]: assigned
> [    0.585003] pci 0000:00:02.0: BAR 1 [mem 0x5000b000-0x5000b0ff]: assigned
> [    0.585119] pci 0000:00:03.0: BAR 0 [io  0x18800400-0x188004ff]: assigned
> [    0.585235] pci 0000:00:03.0: BAR 1 [mem 0x5000b100-0x5000b1ff]: assigned
> [    0.586040] clocksource: Switched to clocksource MIPS
> [    0.595022] NET: Registered PF_INET protocol family
> [    0.596277] IP idents hash table entries: 2048 (order: 2, 16384 bytes, linear)
> [    0.599075] tcp_listen_portaddr_hash hash table entries: 1024 (order: 0, 4096 bytes, linear)
> [    0.599207] Table-perturb hash table entries: 65536 (order: 6, 262144 bytes, linear)
> [    0.599357] TCP established hash table entries: 1024 (order: 0, 4096 bytes, linear)
> [    0.599483] TCP bind hash table entries: 1024 (order: 1, 8192 bytes, linear)
> [    0.599665] TCP: Hash tables configured (established 1024 bind 1024)
> [    0.600026] UDP hash table entries: 256 (order: 1, 8192 bytes, linear)
> [    0.600186] UDP-Lite hash table entries: 256 (order: 1, 8192 bytes, linear)
> [    0.601161] NET: Registered PF_UNIX/PF_LOCAL protocol family
> [    0.603686] RPC: Registered named UNIX socket transport module.
> [    0.603736] RPC: Registered udp transport module.
> [    0.603769] RPC: Registered tcp transport module.
> [    0.603802] RPC: Registered tcp-with-tls transport module.
> [    0.603835] RPC: Registered tcp NFSv4.1 backchannel transport module.
> [    0.603971] PCI: CLS 16 bytes, default 16
> [    0.607134] workingset: timestamp_bits=30 max_order=13 bucket_order=0
> [    0.613358] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
> [    0.621159] printk: legacy console [ttyS0] disabled
> [    0.622542] serial8250.0: ttyS0 at MMIO 0x18058000 (irq = 104, base_baud = 12499875) is a 16550A
> [    0.622738] printk: legacy console [ttyS0] enabled
> [    1.299755] scsi host0: pata-rb532-cf
> [    1.305007] ata1: PATA max PIO4 irq 149 lpm-pol 0
> [    1.313888] eth0: korina-0.20 15Sep2017
> [    1.318861] via-rhine 0000:00:02.0: enabling device (0080 -> 0083)
> [    1.334840] via-rhine 0000:00:02.0 eth1: VIA Rhine III at (ptrval), 00:0c:42:0a:7d:d4, IRQ 142
> [    1.345448] via-rhine 0000:00:02.0 eth1: MII PHY found at address 1, status 0x7849 advertising 05e1 Link 0000
> [    1.356989] via-rhine 0000:00:03.0: enabling device (0080 -> 0083)
> [    1.372559] via-rhine 0000:00:03.0 eth2: VIA Rhine III at (ptrval), 00:0c:42:0a:7d:d5, IRQ 143
> [    1.383162] via-rhine 0000:00:03.0 eth2: MII PHY found at address 1, status 0x7849 advertising 05e1 Link 0000
> [    1.395174] rc32434_wdt: Stopped watchdog timer
> [    1.401166] rc32434_wdt: Watchdog Timer version 1.0, timer margin: 20 sec
> [    1.410007] NET: Registered PF_PACKET protocol family
> [    1.488756] korina korina eth0: link up, 100Mbps, full-duplex, lpa 0xFFFFFF6F
> [    1.514213] Sending DHCP requests ., OK
> [    1.542622] IP-Config: Got DHCP answer from 192.168.1.254, my address is 192.168.1.9
> [    1.551409] IP-Config: Complete:
> [    1.555148]      device=eth0, hwaddr=00:0c:42:0a:7d:d3, ipaddr=192.168.1.9, mask=255.255.255.0, gw=192.168.1.254
> [    1.566657]      host=192.168.1.9, domain=, nis-domain=(none)
> [    1.573201]      bootserver=192.168.1.254, rootserver=192.168.1.254, rootpath=
> [    1.573275]      nameserver0=192.168.1.254
> [    1.588787] check access for rdinit=/init failed: -2, ignoring
> [    1.658499] VFS: Mounted root (nfs filesystem) on device 0:13.
> [    1.667866] devtmpfs: mounted
> [    1.671780] Freeing unused kernel image (initmem) memory: 152K
> [    1.677854] This architecture does not have kernel memory protection.
> [    1.684548] Run /sbin/init as init process
> [    1.688861]   with arguments:
> [    1.688920]     /sbin/init
> [    1.688977]   with environment:
> [    1.689027]     HOME=/
> [    1.689082]     TERM=linux
> [    1.689137]     gpio=16383
> [    1.689193]     board=500
> [    1.689248]     boot=1
> [    1.723116] process '/bin/busybox' started with executable stack
> [  208.334338] random: crng init done