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Subject: Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory
 size
To:     Ramon Fried <ramon.fried@gmail.com>, benh@kernel.crashing.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linuxppc-dev@lists.ozlabs.org,
        open list <linux-kernel@vger.kernel.org>,
        iommu@lists.linux-foundation.org, hch@lst.de, linux@roeck-us.net
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From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <bb76b9a1-dc3a-2357-a871-291d68703776@arm.com>
Date:   Mon, 19 Nov 2018 15:50:35 +0000
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On 19/11/2018 14:18, Ramon Fried wrote:
> On Tue, Oct 9, 2018 at 8:02 AM Benjamin Herrenschmidt
> <benh@kernel.crashing.org> wrote:
>>
>> On Wed, 2018-10-03 at 16:10 -0700, Alexander Duyck wrote:
>>>> -        * Because 32-bit DMA masks are so common we expect every architecture
>>>> -        * to be able to satisfy them - either by not supporting more physical
>>>> -        * memory, or by providing a ZONE_DMA32.  If neither is the case, the
>>>> -        * architecture needs to use an IOMMU instead of the direct mapping.
>>>> -        */
>>>> -       if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
>>>> +       u64 min_mask;
>>>> +
>>>> +       if (IS_ENABLED(CONFIG_ZONE_DMA))
>>>> +               min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
>>>> +       else
>>>> +               min_mask = DMA_BIT_MASK(32);
>>>> +
>>>> +       min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
>>>> +
>>>> +       if (mask >= phys_to_dma(dev, min_mask))
>>>>                   return 0;
>>>> -#endif
>>>>           return 1;
>>>>    }
>>>
>>> So I believe I have run into the same issue that Guenter reported. On
>>> an x86_64 system w/ Intel IOMMU. I wasn't able to complete boot and
>>> all probe attempts for various devices were failing with -EIO errors.
>>>
>>> I believe the last mask check should be "if (mask < phys_to_dma(dev,
>>> min_mask))" not a ">=" check.
>>
>> Right, that test is backwards. I needed to change it here too (powermac
>> with the rest of the powerpc series).
>>
>> Cheers,
>> Ben.
>>
>>
> 
> Hi, I'm working on a MIPS64 soc with PCIe root complex on it, and it
> appears that this series of patches are causing all PCI drivers that
> request 64bit mask to fail with -5.
> It's broken in 4.19. However, I just checked, it working on master.
> We may need to backport a couple of patches to 4.19. I'm not sure
> though which patches should be backported as there were at least 10
> patches resolving this dma_direct area recently.
> Christoph, Robin.
> Can we ask Greg to backport all these changes ? What do you think ?

As far as I'm aware, the only real issue in 4.19 was my subtle breakage 
around setting bus_dma_mask - that's fixed by 6778be4e5209, which 
according to my inbox got picked up by autosel for 4.19 stable last week.

Robin.