linux-kernel - [PATCH 4.18 053/228] powerpc/powernv/ioda2: Reduce upper limit for DMA window size

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Message-Id: <20181002132502.776650588@linuxfoundation.org>
Date:   Tue,  2 Oct 2018 06:22:30 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alexey Kardashevskiy <aik@...abs.ru>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.18 053/228] powerpc/powernv/ioda2: Reduce upper limit for DMA window size

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Kardashevskiy <aik@...abs.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 levels requested"
Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/powerpc/platforms/powernv/pci-ioda.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -2841,7 +2841,7 @@ static long pnv_pci_ioda2_table_alloc_pa
 	level_shift = entries_shift + 3;
 	level_shift = max_t(unsigned, 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 */