linux-kernel - [PATCH v2] swiotlb: Make SWIOTLB_NO

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Date:   Sat, 20 Mar 2021 20:37:40 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org (open list:SWIOTLB SUBSYSTEM)
Subject: [PATCH v2] swiotlb: Make SWIOTLB_NO_FORCE perform no allocation

When SWIOTLB_NO_FORCE is used, there should really be no allocations of
default_nslabs to occur since we are not going to use those slabs. If a
platform was somehow setting swiotlb_no_force and a later call to
swiotlb_init() was to be made we would still be proceeding with
allocating the default SWIOTLB size (64MB), whereas if swiotlb=noforce
was set on the kernel command line we would have only allocated 2KB.

This would be inconsistent and the point of initializing default_nslabs
to 1, was intended to allocate the minimum amount of memory possible, so
simply remove that minimal allocation period.

Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
Changes in v2:

- rebased against devel/for-linus-5.13
- updated commit message to reflect variable names

 kernel/dma/swiotlb.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 539c76beb52e..d20002a61546 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -83,12 +83,10 @@ setup_io_tlb_npages(char *str)
 	}
 	if (*str == ',')
 		++str;
-	if (!strcmp(str, "force")) {
+	if (!strcmp(str, "force"))
 		swiotlb_force = SWIOTLB_FORCE;
-	} else if (!strcmp(str, "noforce")) {
+	else if (!strcmp(str, "noforce"))
 		swiotlb_force = SWIOTLB_NO_FORCE;
-		default_nslabs = 1;
-	}
 
 	return 0;
 }
@@ -211,6 +209,9 @@ swiotlb_init(int verbose)
 	size_t bytes = PAGE_ALIGN(default_nslabs << IO_TLB_SHIFT);
 	void *tlb;
 
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		return;
+
 	/* Get IO TLB memory from the low pages */
 	tlb = memblock_alloc_low(bytes, PAGE_SIZE);
 	if (!tlb)
-- 
2.25.1