linux-kernel - [PATCH] swiotlb: Make SWIOTLB_NO

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Message-Id: <20210319040055.183433-1-f.fainelli@gmail.com>
Date:   Thu, 18 Mar 2021 21:00:54 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     opendmb@...il.com, 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] swiotlb: Make SWIOTLB_NO_FORCE perform no allocation

When SWIOTLB_NO_FORCE is used, there should really be no allocations of
io_tlb_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 io_tlb_nslabs
to 1, was to avoid hitting the test for io_tlb_nslabs being 0/not
initialized.

Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
 kernel/dma/swiotlb.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index c10e855a03bc..526c8321b76f 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -121,12 +121,10 @@ 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;
-		io_tlb_nslabs = 1;
-	}
 
 	return 0;
 }
@@ -284,6 +282,9 @@ swiotlb_init(int verbose)
 	unsigned char *vstart;
 	unsigned long bytes;
 
+	if (swiotlb_force == SWIOTLB_NO_FORCE)
+		goto out;
+
 	if (!io_tlb_nslabs) {
 		io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
 		io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
@@ -302,6 +303,7 @@ swiotlb_init(int verbose)
 		io_tlb_start = 0;
 	}
 	pr_warn("Cannot allocate buffer");
+out:
 	no_iotlb_memory = true;
 }
 
-- 
2.25.1