Re: [PATCH v2 0/9] PCI: rockchip: Fix RK3399 PCIe endpoint controller driver

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 3/14/23 23:53, Rick Wertenbroek wrote:
> Hello Damien,
> I also noticed random issues I suspect to be related to link status or power
> state, in my case it sometimes happens that the BARs (0-6) in the config
> space get reset to 0. This is not due to the driver because the driver never
> ever accesses these registers (@0xfd80'0010 to 0xfd80'0024 TRM
> 17.6.4.1.5-17.6.4.1.10).
> I don't think the host rewrites them because lspci shows the BARs as
> "[virtual]" which means they have been assigned by host but have 0
> value in the endpoint device (when lspci rereads the PCI config header).
> See https://github.com/pciutils/pciutils/blob/master/lspci.c#L422
> 
> So I suspect the controller detects something related to link status or
> power state and internally (in hardware) resets those registers. It's not
> the kernel code, it never accesses these regs. The problem occurs
> very randomly, sometimes in a few seconds, sometimes I cannot see
> it for a whole day.
> 
> Is this similar to what you are experiencing ?

Yes. I sometimes get NMIs after starting the function driver, when my function
driver starts probing the bar registers after seeing the host changing one
register. And the link also comes up with 4 lanes or 2 lanes, random.

> Do you have any idea as to what could make these registers to be reset
> (I could not find anything in the TRM, also nothing in the driver seems to
> cause it).

My thinking is that since we do not have a linkup notifier, the function driver
starts setting things up without the link established (e.g. when the host is
still powered down). Once the host start booting and pic link is established,
things may be reset in the hardware... That is the only thing I can think of.

And yes, there are definitely something going on with the power states too I
think: if I let things idle for a few minutes, everything stops working: no
activity seen on the endpoint over the BARs. I tried enabling the sys and client
interrupts to see if I can see power state changes, or if clearing the
interrupts helps (they are masked by default), but no change. And booting the
host with pci_aspm=off does not help either. Also tried to change all the
capabilities related to link & power states to "off" (not supported), and no
change either. So currently, I am out of ideas regarding that one.

I am trying to make progress on my endpoint driver (nvme function) to be sure it
is not a bug there that breaks things. I may still have something bad because
when I enable the BIOS native NVMe driver on the host, either the host does not
boot, or grub crashes with memory corruptions. Overall, not yet very stable and
still trying to sort out the root cause of that.


> Do you want me to include this patch in the V3 series or will you
> submit another patch series for the changes you applied on the RK3399 PCIe
> endpoint controller ? I don't know if you prefer to build the V3
> together or if you
> prefer to submit another patch series on top of mine. Let me know.

If it is no trouble, please include it with your series. Will be easier to
retest everything together :)

-- 
Damien Le Moal
Western Digital Research