[RFC PATCH kernel] powerpc/ioda: Set "read" permission when "write" is set

[Douglas Miller]

We finally got the chance to test it end of last week. I forgot to 
update everyone Monday. B all appearances, the patch fixes the problem. 
We did not see any new issues with the patch (vs. same test scenarios 
without).

I'll also update the bugzilla.

Thanks,
Doug

On 02/08/2016 07:37 PM, Alexey Kardashevskiy wrote:
> On 01/20/2016 06:01 AM, Douglas Miller wrote:
>>
>>
>> On 01/18/2016 09:52 PM, Alexey Kardashevskiy wrote:
>>> On 01/13/2016 01:24 PM, Douglas Miller wrote:
>>>>
>>>>
>>>> On 01/12/2016 05:07 PM, Benjamin Herrenschmidt wrote:
>>>>> On Tue, 2016-01-12 at 15:40 +1100, Alexey Kardashevskiy wrote:
>>>>>> Quite often drivers set only "write" permission assuming that this
>>>>>> includes "read" permission as well and this works on plenty
>>>>>> platforms.
>>>>>> However IODA2 is strict about this and produces an EEH when "read"
>>>>>> permission is not and reading happens.
>>>>>>
>>>>>> This adds a workaround in IODA code to always add the "read" bit 
>>>>>> when
>>>>>> the "write" bit is set.
>>>>>>
>>>>>> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>>>>>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>>>>>> ---
>>>>>>
>>>>>>
>>>>>> Ben, what was the driver which did not set "read" and caused EEH?
>>>>> aacraid
>>>>>
>>>>> Cheers,
>>>>> Ben.
>>>> Just to be precise, the driver wasn't responsible for setting READ. 
>>>> The
>>>> driver called scsi_dma_map() and the scsicmd was set (by scsi 
>>>> layer) as
>>>> DMA_FROM_DEVICE so the current code would set the permissions to
>>>> WRITE-ONLY. Previously, and in other architectures, this scsicmd 
>>>> would have
>>>> resulted in READ+WRITE permissions on the DMA map.
>>>
>>>
>>> Does the patch fix the issue? Thanks.
>>>
>>>
>>>
>>>>>
>>>>>> ---
>>>>>>   arch/powerpc/platforms/powernv/pci.c | 6 ++++++
>>>>>>   1 file changed, 6 insertions(+)
>>>>>>
>>>>>> diff --git a/arch/powerpc/platforms/powernv/pci.c
>>>>>> b/arch/powerpc/platforms/powernv/pci.c
>>>>>> index f2dd772..c7dcae5 100644
>>>>>> --- a/arch/powerpc/platforms/powernv/pci.c
>>>>>> +++ b/arch/powerpc/platforms/powernv/pci.c
>>>>>> @@ -601,6 +601,9 @@ int pnv_tce_build(struct iommu_table *tbl, long
>>>>>> index, long npages,
>>>>>>       u64 rpn = __pa(uaddr) >> tbl->it_page_shift;
>>>>>>       long i;
>>>>>> +    if (proto_tce & TCE_PCI_WRITE)
>>>>>> +        proto_tce |= TCE_PCI_READ;
>>>>>> +
>>>>>>       for (i = 0; i < npages; i++) {
>>>>>>           unsigned long newtce = proto_tce |
>>>>>>               ((rpn + i) << tbl->it_page_shift);
>>>>>> @@ -622,6 +625,9 @@ int pnv_tce_xchg(struct iommu_table *tbl, long
>>>>>> index,
>>>>>>       BUG_ON(*hpa & ~IOMMU_PAGE_MASK(tbl));
>>>>>> +    if (newtce & TCE_PCI_WRITE)
>>>>>> +        newtce |= TCE_PCI_READ;
>>>>>> +
>>>>>>       oldtce = xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce));
>>>>>>       *hpa = be64_to_cpu(oldtce) & ~(TCE_PCI_READ |
>>>>>> TCE_PCI_WRITE);
>>>>>>       *direction = iommu_tce_direction(oldtce);
>>>>> _______________________________________________
>>>>> Linuxppc-dev mailing list
>>>>> Linuxppc-dev at lists.ozlabs.org
>>>>> https://lists.ozlabs.org/listinfo/linuxppc-dev
>>>>
>>>> _______________________________________________
>>>> Linuxppc-dev mailing list
>>>> Linuxppc-dev at lists.ozlabs.org
>>>> https://lists.ozlabs.org/listinfo/linuxppc-dev
>>>
>>>
>> I am still working on getting a machine to try this on. From code
>> inspection, it looks like it should work. The problem is shortage of
>> machines and machines tied-up by Test.
>
> Any progress here? Thanks.
>
>
>
>