Re: [PATCH kernel v2 0/2] powerpc/ioda2: Another attempt to allow DMA masks between 32 and 59

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 01/05/2019 16:09, Alistair Popple wrote:
> Hi Alexey,
> 
> Do we need a seperate patch to allow this to be used? Last time I tried 
> calling dma_set_mask(52) on powernv it returned an error and there doesn't 
> seem to be anything obvious to me in this series to change that behaviour, but 
> perhaps I missed something.


Right now (this could have changed with the Hellwig's patches) when
called with MASK(52), dma_iommu_dma_supported() will select the default
ops and allow any mask. The kernel won't be able to use the entire mask
(since the default window won't be that big) and eventually
dma_map_ops::alloc() will fail when the entire DMA window is used but
this may happen anyway. This patchset does not change this behaviour,
just moves the upper limit for DMA window further up.



https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kernel/dma-iommu.c?h=v5.1-rc7#n117

int dma_iommu_dma_supported(struct device *dev, u64 mask)
{
	struct iommu_table *tbl = get_iommu_table_base(dev);

	if (!tbl) {
		dev_info(dev, "Warning: IOMMU dma not supported: mask 0x%08llx"
			", table unavailable\n", mask);
		return 0;
	}

	if (dev_is_pci(dev) && dma_iommu_bypass_supported(dev, mask)) {
		dev->archdata.iommu_bypass = true;
		dev_dbg(dev, "iommu: 64-bit OK, using fixed ops\n");
		return 1;
	}

	if (tbl->it_offset > (mask >> tbl->it_page_shift)) {
		dev_info(dev, "Warning: IOMMU offset too big for device mask\n");
		dev_info(dev, "mask: 0x%08llx, table offset: 0x%08lx\n",
				mask, tbl->it_offset << tbl->it_page_shift);
		return 0;
	}

	dev_dbg(dev, "iommu: not 64-bit, using default ops\n");
	dev->archdata.iommu_bypass = false;
	return 1;
}


> 
> - Alistair
> 
> On Wednesday, 1 May 2019 3:28:20 PM AEST Alexey Kardashevskiy wrote:
>> This is an attempt to allow DMA masks between 32..59 which are not large
>> enough to use either a PHB3 bypass mode or a sketchy bypass. Depending
>> on the max order, up to 40 is usually available.
>>
>>
>> This is based on sha1
>> 37624b58542f Linus Torvalds "Linux 5.1-rc7".
>>
>> Please comment. Thanks.
>>
>>
>>
>> Alexey Kardashevskiy (2):
>>   powerpc/powernv/ioda2: Allocate TCE table levels on demand for default
>>     DMA window
>>   powerpc/powernv/ioda2: Create bigger default window with 64k IOMMU
>>     pages
>>
>>  arch/powerpc/include/asm/iommu.h              |  8 ++-
>>  arch/powerpc/platforms/powernv/pci.h          |  2 +-
>>  arch/powerpc/kernel/iommu.c                   | 58 +++++++++++++------
>>  arch/powerpc/platforms/powernv/pci-ioda-tce.c | 20 +++----
>>  arch/powerpc/platforms/powernv/pci-ioda.c     | 40 +++++++++++--
>>  5 files changed, 90 insertions(+), 38 deletions(-)
> 
> 

-- 
Alexey