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powerpc/powernv/ioda2: Reduce upper limit for DMA window size (again)

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mpe: This was fixed originally in commit d3d4ffaae4
("powerpc/powernv/ioda2: Reduce upper limit for DMA window size"), but
contrary to what the merge commit says was inadvertently lost by me in
commit ce57c6610c ("Merge branch 'topic/ppc-kvm' into next") which
brought in changes that moved the code to a new file. So reapply it to
the new file.

Original commit message follows:

We use PHB in mode1 which uses bit 59 to select a correct DMA window.
However there is mode2 which uses bits 59:55 and allows up to 32 DMA
windows per a PE.

Even though documentation does not clearly specify that, it seems that
the actual hardware does not support bits 59:55 even in mode1, in
other words we can create a window as big as 1<<58 but DMA simply
won't work.

This reduces the upper limit from 59 to 55 bits to let the userspace
know about the hardware limits.

Fixes: ce57c6610c ("Merge branch 'topic/ppc-kvm' into next")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Alexey Kardashevskiy 2018-09-11 15:38:05 +10:00 committed by Michael Ellerman
parent 51c3c62b58
commit 7233b8cab3
1 changed files with 1 additions and 1 deletions
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arch/powerpc/platforms/powernv/pci-ioda-tce.c
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@ -276,7 +276,7 @@ long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset,
level_shift = entries_shift + 3;
level_shift = max_t(unsigned int, level_shift, PAGE_SHIFT);
if ((level_shift - 3) * levels + page_shift >= 60)
if ((level_shift - 3) * levels + page_shift >= 55)
return -EINVAL;
/* Allocate TCE table */