DMA Mapping Error in ppc64

[Jared Bents]

Thank you for the advice.  Looks like I get to try to rewrite the ath9k and
ath10k drivers to use dma_alloc_coherent() instead of kmemdup() and
dev_alloc_skb()

On Thu, Mar 22, 2018 at 8:19 PM, Oliver <oohall at gmail.com> wrote:

> On Fri, Mar 23, 2018 at 1:37 AM, Jared Bents
> <jared.bents at rockwellcollins.com> wrote:
> > Thank you for the response but unfortunately, it looks like I already
> > have that and it is being used.  To verify, I commented that out and
> > got the failure "dma_direct_alloc_coherent: No suitable zone for pfn
> > 0xe0000".  Below is the code flow for function
> > ath10k_pci_hif_exchange_bmi_msg which is showing the first dma mapping
> > error.
> >
> > ath10k_pci_hif_exchange_bmi_msg -> dma_map_single ->
> > dma_map_single_attrs -> swiotlb_map_page -> dma_capable (returns
> > false)
> >
> >
> > dma_capable is what reports the failure in that flow.
> >
> > static inline bool dma_capable(struct device *dev, dma_addr_t addr,
> size_t size)
> > {
> > #ifdef CONFIG_SWIOTLB
> >     struct dev_archdata *sd = &dev->archdata;
> >
> >    if (sd->max_direct_dma_addr && addr + size > sd->max_direct_dma_addr)
> >         return false;
> > #endif
> >
> >     if (!dev->dma_mask)
> >         return false;
> >
> >     return addr + size - 1 <= *dev->dma_mask;
> > }
> > Getting the below values:
> > addr = 1ee376218
> > size = 4
> > sd->max_direct_dma_addr = e0000000 which is I believe DMA window size
> (e0000000)
> >
> > when executed sd->max_direct_dma_addr(e0000000) && addr(1ee376218) +
> > size(4) becomes e0000004 which is > sd->max_direct_dma_addr (e0000000)
> >
> >
> > So even though limit_zone_pfn(ZONE_DMA32, 1UL << (31 - PAGE_SHIFT)) is
> > being used in arch/powerpc/platforms/85xx/corenet_generic.c,
>
> > kmemdup(req, req_len, GFP_KERNEL) is returning an address that when
> > sent to dma_map_single(), results in a bad map.
>
> You need to use (GFP_KERNEL | GFP_DMA32) to constrain the allocations
> to ZONE_DMA32. Without that the kmemdup() will allocate from any zone
> so you'll probably get an unmappable address.
>
> That said, the driver probably shouldn't be using kmemdup() here.
> DMA-API.txt pretty explicitly says that drivers should not assume that
> dma_map_single() will work with arbitrary memory. It should be using
> dma_alloc_coherent() or a dma pool here.
>
> > - Jared
> >
> > On Wed, Mar 21, 2018 at 11:54 PM, Oliver <oohall at gmail.com> wrote:
> >> On Thu, Mar 22, 2018 at 8:00 AM, Jared Bents
> >> <jared.bents at rockwellcollins.com> wrote:
> >>> Hi all,
> >>>
> >>> Apologies for the amount of information but we've been debugging this
> >>> for a while and I wanted to get what we are seeing captured as much as
> >>> possible.  We are a T1042 processor and have a total 8GB DDR and our
> >>> kernel version is fsl-sdk-v2.0-1703 (linux v4.1.35) as that is the
> >>> latest version supplied by NXP.
> >>>
> >>> A while ago we ported from 32 bit to 64 bit.  Everything continued to
> >>> work except the ath10k module we have.  So as a first step, we checked
> >>> to see if an ath9k module also failed to work and it was also no
> >>> longer working.  The ath10k is working fine on a 32 bit system but
> >>> it's not working on 64 bit system as we are getting dma mapping errors
> >>> when trying to initialize the wifi modules.
> >>>
> >>> pci_bus 0002:01: bus scan returning with max=01
> >>> pci_bus 0002:01: busn_res: [bus 01] end is updated to 01
> >>> pci_bus 0002:00: bus scan returning with max=01
> >>> ath10k_pci 0000:01:00.0: unable to get target info from device
> >>> ath10k_pci 0000:01:00.0: could not get target info (-5)
> >>> ath10k_pci 0000:01:00.0: could not probe fw (-5)
> >>> ath10k_pci 0001:01:00.0: Direct firmware load for
> >>> ath10k/cal-pci-0001:01:00.0.bin failed with error -2
> >>>
> >>>
> >>> First, we have tried the mainline kernel (v4.15)  to see if that would
> >>> fix the issue, it did not.  So I made a patch for the ath10k driver to
> >>> restrict to just GFP_DMA areas when allocating memory or creating
> >>> sk_buffs and have attached it.  The ath10k wifi modules now initialize
> >>> correctly but when I try to connect them and send traffic, they get a
> >>> DMA mapping error from the sk_buff that it receives from elsewhere in
> >>> the kernel.  So while the driver appears to be fixable with the patch,
> >>> the modules are still unusable due to data being sent to the driver
> >>> when ath10k_tx is called and it tries to dma map with the provided
> >>> skb.  Also, according to the ath10k mailing list, GFP_DMA is not
> >>> supposed to be used in general.  The error below is the same sort of
> >>> dma mapping error that is seen when initializing the modules without
> >>> the patch to OR with GFP_DMA.
> >>>
> >>> ath10k_pci 0001:01:00.0: failed to transmit packet, dropping: -5
> >>>
> >>>
> >>> We asked on the ath10k mailing list if anyone else is having this
> >>> problem and no one else seems to have the issue but they are using
> >>> different architectures (ARM or X86). As a result, it does not seem to
> >>> be a driver issue to us but something within the PowerPC arch.  So we
> >>> dug a little deeper to try to find what addresses being mapped are
> >>> working and what address being mapped are not working.
> >>>
> >>> We found that when the virtual address of data pointer (a member of
> >>> sk_buff) is above ~3.7 GB RAM address range then return address from
> >>> dma_map_single API is failed to validate in dma_mapping_error
> >>> function.
> >>>
> >>> We also noticed that in a 64bit machine sometimes ping is working and
> >>> because of the virtual address is under ~3.7GAM RAM address range.  So
> >>> if we set mem=2048M in the bootargs, the ath10k module works
> >>> perfectly, however this isn't a real solution since it cuts our
> >>> available RAM from 8GB to 2GB.
> >>
> >> I think there's a known issue with the freescale PCIe root complex
> >> where it can't DMA beyond the 4GB mark. There's a workaround in
> >> the form of limit_zone_pfn() which you can use to put the lower 4GB into
> >> ZONE_DMA32 and allocate from there rather than ZONE_NORMAL.
> >> For details of how to use it have a look at corenet_gen_setup_arch() in
> >> arch/powerpc/platforms/85xx/corenet_generic.c
> >>
> >> Hope that helps,
> >> Oliver
>
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