Re: dwc3 initiated xhci probe problem in arm64 4.4 kernel due to DMA setup

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Catalin Marinas <catalin.marinas@xxxxxxx> writes:
> On Fri, Apr 15, 2016 at 11:01:08AM +0100, Catalin Marinas wrote:
>> On Fri, Apr 15, 2016 at 12:49:15PM +0300, Felipe Balbi wrote:
>> > Catalin Marinas <catalin.marinas@xxxxxxx> writes:
>> > > On Thu, Apr 14, 2016 at 12:46:47PM +0000, David Fisher wrote:
>> > >> dwc3 is in dual-role, with "synopsys,dwc3" specified in DT.
>> > >> 
>> > >> When xhci is probed, initiated from dwc3/host.c (not DT), we get :
>> > >> xhci-hcd: probe of xhci-hcd.7.auto failed with error -5
>> > >> This -EIO error originated from inside dma_set_mask() down in include/asm-generic/dma-mapping-common.h
>> > >> 
>> > >> If "generic-xhci" is specified in DT instead, it probes fine as a host-only dwc3
>> > >> The difference between DT initiated probe and dwc3 initiated probe is that
>> > >> when DT initiated probe gets to dma_supported, dma_supported is 
>> > >> implemented by swiotlb_dma_supported (previously set up by a DT call to arch_dma_setup_ops).
>> > >> Whereas when dwc3 initiated xhci probe gets to dma_supported, arch_dma_setup_ops has not been called 
>> > >> and dma_supported is only implemented by __dummy_dma_supported, returning 0.
>> > >> 
>> > >> Bisecting finds the "bad" commit as 
>> > >> 1dccb598df549d892b6450c261da54cdd7af44b4  (inbetween 4.4-rc1 and 4.4-rc2)
>> > >> --- a/arch/arm64/include/asm/dma-mapping.h
>> > >> --- a/arch/arm64/mm/dma-mapping.c
>> > >> 
>> > >> Previous to this commit, dma_ops = &swiotlb_dma_ops was done in arm64_dma_init
>> > >> After this commit, the assignment is only done in arch_dma_setup_ops.
>> > >
>> > > This restriction was added on purpose and the arm64 __generic_dma_ops()
>> > > now has a comment:
>> > >
>> > > 	/*
>> > > 	 * We expect no ISA devices, and all other DMA masters are expected to
>> > > 	 * have someone call arch_setup_dma_ops at device creation time.
>> > > 	 */
>> > 
>> > how ?
>> 
>> Usually by calling arch_setup_dma_ops().
>
> Or of_dma_configure(), I forgot to mention this (see the
> pci_dma_configure() function as an example).

the device is manually created, there's not OF/DT for it ;-)

-- 
balbi

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