Snapdragon X55 (Thinkpad X1 Nano w/5G Modem)
Loic Poulain
loic.poulain at linaro.org
Tue May 18 10:25:18 UTC 2021
Hi Oskar,
On Tue, 18 May 2021 at 11:33, Oskar Stenman <oskar at cetex.se> wrote:
>
> Hi!
>
> I'm way out in the deep end of the pool here poking at things i shouldn't
to see what happens and if i can learn something, or find a bit more info
where things go wrong.. So I patched drivers/bus/mhi/pci_generic.c to give
some more debug info:
>
> oskar at oskar-ThinkPad-X1-Nano-Gen-1:~/src/linux-kernel/linux-upstream-5.12.0+$
git diff
> diff --git a/drivers/bus/mhi/pci_generic.c b/drivers/bus/mhi/pci_generic.c
> index 7c810f02a2ef..819c0f17993d 100644
> --- a/drivers/bus/mhi/pci_generic.c
> +++ b/drivers/bus/mhi/pci_generic.c
> @@ -492,9 +492,13 @@ static int mhi_pci_get_irqs(struct mhi_controller
*mhi_cntrl,
> * Alloc one MSI vector for BHI + one vector per event ring,
ideally...
> * No explicit pci_free_irq_vectors required, done by
pcim_release.
> */
> + dev_warn(&pdev->dev, "mhi_cntrl_config->num_events: %d\n",
mhi_cntrl_config->num_events);
> mhi_cntrl->nr_irqs = 1 + mhi_cntrl_config->num_events;
> + dev_warn(&pdev->dev, "mhi_cntrl->nr_irqs: %d\n",
mhi_cntrl->nr_irqs);
> + dev_warn(&pdev->dev, "PCI_IRQ_MSI: %d\n", PCI_IRQ_MSI);
>
> nr_vectors = pci_alloc_irq_vectors(pdev, 1, mhi_cntrl->nr_irqs,
PCI_IRQ_MSI);
> + dev_warn(&pdev->dev, "nr_vectors: %d\n", nr_vectors);
> if (nr_vectors < 0) {
> dev_err(&pdev->dev, "Error allocating MSI vectors %d\n",
> nr_vectors);
>
> Compiling and loading that module prints the following in dmesg:
> [ 5553.096754] mhi-pci-generic 0000:08:00.0: BAR 0: assigned [mem
0xbc200000-0xbc200fff 64bit]
> [ 5553.097033] mhi-pci-generic 0000:08:00.0:
mhi_cntrl_config->num_events: 4
> [ 5553.097036] mhi-pci-generic 0000:08:00.0: mhi_cntrl->nr_irqs: 5
> [ 5553.097038] mhi-pci-generic 0000:08:00.0: PCI_IRQ_MSI: 2
> [ 5553.097314] mhi-pci-generic 0000:08:00.0: nr_vectors: 1 <- requested
5, got 1..
> [ 5553.097316] mhi-pci-generic 0000:08:00.0: using shared MSI
>
> requesting 5 nr_vectors, getting one which then seems to trigger another
codepath..
>
> Whlie researching pci_alloc_irq_vectors I then found this semi-related
thread
https://stackoverflow.com/questions/49821599/multiple-msi-vectors-linux-pci-alloc-irq-vectors-return-one-while-the-devi
where Riton38 mentions that enabling intel vt-d "solved the problem"
(default from factory on this Thinkpad X1 Nano it has all virtualization
disabled).
>
> Since i can't figure out what's wrong with the actual irq-setup as it's
possibly bug in modem firmware (throwing interrupts over some channel when
it shouldn't), or maybe a bug in how irq's are allocated in mhi_pci_generic
i just tried enabling Intel VT-D in bios (security -> virtualization) and
what would you know, it works!!
>
> [ 81.291874] mhi_pci_generic: loading out-of-tree module taints kernel.
> [ 81.291970] mhi_pci_generic: module verification failed: signature
and/or required key missing - tainting kernel
> [ 81.292527] mhi-pci-generic 0000:08:00.0: BAR 0: assigned [mem
0xbc200000-0xbc200fff 64bit]
> [ 81.292560] mhi-pci-generic 0000:08:00.0: enabling device (0000 ->
0002)
> [ 81.292603] mhi-pci-generic 0000:08:00.0:
mhi_cntrl_config->num_events: 4
> [ 81.292605] mhi-pci-generic 0000:08:00.0: mhi_cntrl->nr_irqs: 5
> [ 81.292606] mhi-pci-generic 0000:08:00.0: PCI_IRQ_MSI: 2
> [ 81.292713] mhi-pci-generic 0000:08:00.0: nr_vectors: 5 <- We got 5
vectors now!
> [ 81.292955] mhi mhi0: Requested to power ON
> [ 81.293180] mhi mhi0: Power on setup success
> [ 81.325854] mhi mhi0: Wait for device to enter SBL or Mission mode
>
> After running qmicli and connecting, no more errors in kernel log.
>
> oskar at oskar-ThinkPad-X1-Nano-Gen-1:~/src/linux-kernel/linux-upstream-5.12.0+/drivers/bus/mhi$
ping ftp.sunet.se
> PING ftp.sunet.se(tutankhamon.ftp.acc.umu.se (2001:6b0:19::163)) 56 data
bytes
> 64 bytes from tutankhamon.ftp.acc.umu.se (2001:6b0:19::163): icmp_seq=1
ttl=51 time=46.1 ms
> 64 bytes from tutankhamon.ftp.acc.umu.se (2001:6b0:19::163): icmp_seq=2
ttl=51 time=43.9 ms
> 64 bytes from tutankhamon.ftp.acc.umu.se (2001:6b0:19::163): icmp_seq=3
ttl=51 time=42.7 ms
> 64 bytes from tutankhamon.ftp.acc.umu.se (2001:6b0:19::163): icmp_seq=4
ttl=51 time=49.0 ms
> ^C
> --- ftp.sunet.se ping statistics ---
> 4 packets transmitted, 4 received, 0% packet loss, time 3005ms
> rtt min/avg/max/mdev = 42.708/45.419/49.019/2.404 ms
>
> Speedtest now gives decent speed, 50Mbit/s down and 13.4Mbit/ up where i
before only got +1000ms latency and 7Mbit/s down where I am (just outside
of central stockholm)
> https://www.speedtest.net/result/11435773983
>
> Anything i can do to test / debug interrupts without intel vt-d enabled
while I have this fresh in memory?
Yes, without intel VT-D (and IRQ_REMAP kernel config), it's not possible to
request multiple MSI, that's indeed why you get the warning. Normally, each
MHI event ring has its own dedicated MSI (to isolate events). But because
we noticed vt-d is not necessarily enabled by default, we introduced a
fallback to use a single shared MSI. That also why you get multiple irq
names (bhi, mhi, mhi....) for the same IRQ index:
>> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5
CPU6 CPU7
>> 143: 0 0 0 0 0 6
0 192 PCI-MSI 4194304-edge bhi, mhi, mhi, mhi, mhi
related patch:
https://git.kernel.org/pub/scm/linux/kernel/git/mani/mhi.git/commit/?h=mhi-next&id=b91c3b30e2267265cd7e67cb3d0c99c48c02b001
This shared IRQ mechanism has been validated with Telit FN980m WWAN module.
In your case, the modem seems to trigger a different interrupt than the
shared one... I would suggest checking in the MHI core, especially in
mhi_init_irq_setup() for the host side and in mhi_init_dev_ctxt() for the
modem side, that misvec index is set to the same value (0).
If everything is correct, it's possibly a bug on modem/firmware side.
Regards,
Loic
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