DMA Mapping Error in ppc64

[Oliver]

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