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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Alexey Kardashevskiy <aik@ozlabs.ru>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.14 41/87] powerpc/powernv/ioda2: Reduce upper limit
 for DMA window size
Thread-Topic: [PATCH AUTOSEL 4.14 41/87] powerpc/powernv/ioda2: Reduce upper
 limit for DMA window size
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Date:   Mon, 17 Sep 2018 03:02:49 +0000
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From: Alexey Kardashevskiy <aik@ozlabs.ru>

[ Upstream commit d3d4ffaae439981e1e441ebb125aa3588627c5d8 ]

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: 7aafac11e3 "powerpc/powernv/ioda2: Gracefully fail if too many TCE l=
evels requested"
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 arch/powerpc/platforms/powernv/pci-ioda.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platf=
orms/powernv/pci-ioda.c
index e919696c7137..ddef22e00ddd 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -2787,7 +2787,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, =
__u64 bus_offset,
 	level_shift =3D entries_shift + 3;
 	level_shift =3D max_t(unsigned, level_shift, PAGE_SHIFT);
=20
-	if ((level_shift - 3) * levels + page_shift >=3D 60)
+	if ((level_shift - 3) * levels + page_shift >=3D 55)
 		return -EINVAL;
=20
 	/* Allocate TCE table */
--=20
2.17.1