Re: [PATCH v4 4/7] s390/pci: Use dma-iommu layer

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 1/19/23 11:33 AM, Niklas Schnelle wrote:
> On Tue, 2023-01-17 at 10:09 -0500, Matthew Rosato wrote:
>> On 1/4/23 7:05 AM, Niklas Schnelle wrote:
>>> While s390 already has a standard IOMMU driver and previous changes have
>>> added I/O TLB flushing operations this driver is currently only used for
>>> user-space PCI access such as vfio-pci. For the DMA API s390 instead
>>> utilizes its own implementation in arch/s390/pci/pci_dma.c which drives
>>> the same hardware and shares some code but requires a complex and
>>> fragile hand over between DMA API and IOMMU API use of a device and
>>> despite code sharing still leads to significant duplication and
>>> maintenance effort. Let's utilize the common code DMAP API
>>> implementation from drivers/iommu/dma-iommu.c instead allowing us to
>>> get rid of arch/s390/pci/pci_dma.c.
>>>
>>> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
>>> diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
>>> index ef38b1514c77..6b0fe8761509 100644
>>> --- a/arch/s390/pci/pci.c
>>> +++ b/arch/s390/pci/pci.c
>>> @@ -124,7 +124,11 @@ int zpci_register_ioat(struct zpci_dev *zdev, u8 dmaas,
>>>  
>>>  	WARN_ON_ONCE(iota & 0x3fff);
>>>  	fib.pba = base;
>>> -	fib.pal = limit;
>>> +	/* Work around off by one in ISM virt device */
>>> +	if (zdev->pft == 0x5 && limit > base)
>>
>> Nit: maybe a named #define for the ISM pft rather than hard-coding 0x5 here
>>
> 
> Hmm, I agree in principle but not sure where to put this #define. Maybe

I would suggest pci_clp.h since the value is coming from a clp.

> also important to mention that the off-by-one has actually been fixed
> in current firmware but of course we still have to support broken
> devices and the workaround still works with fixed ISM.

+1