linux-kernel - [PATCH v1 03/10] powerpc/kernel/iommu: Use largepool as a last resort when !largealloc

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Message-Id: <20200817234033.442511-4-leobras.c@gmail.com>
Date:   Mon, 17 Aug 2020 20:40:26 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Christophe Leroy <christophe.leroy@....fr>,
        Leonardo Bras <leobras.c@...il.com>,
        Joel Stanley <joel@....id.au>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>,
        Brian King <brking@...ux.vnet.ibm.com>,
        Murilo Fossa Vicentini <muvic@...ux.ibm.com>,
        David Dai <zdai@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1 03/10] powerpc/kernel/iommu: Use largepool as a last resort when !largealloc

As of today, doing iommu_range_alloc() only for !largealloc (npages <= 15)
will only be able to use 3/4 of the available pages, given pages on
largepool  not being available for !largealloc.

This could mean some drivers not being able to fully use all the available
pages for the DMA window.

Add pages on largepool as a last resort for !largealloc, making all pages
of the DMA window available.

Signed-off-by: Leonardo Bras <leobras.c@...il.com>
---
 arch/powerpc/kernel/iommu.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index d7086087830f..7f603d4e62d4 100644
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -261,6 +261,15 @@ static unsigned long iommu_range_alloc(struct device *dev,
 			pass++;
 			goto again;
 
+		} else if (pass == tbl->nr_pools + 1) {
+			/* Last resort: try largepool */
+			spin_unlock(&pool->lock);
+			pool = &tbl->large_pool;
+			spin_lock(&pool->lock);
+			pool->hint = pool->start;
+			pass++;
+			goto again;
+
 		} else {
 			/* Give up */
 			spin_unlock_irqrestore(&(pool->lock), flags);
-- 
2.25.4