swiotlb: Add swiotlb=noforce debug option

commit fff5d99225107f5f13fe4a9805adc2a1c4b5fb00 upstream.

On architectures like arm64, swiotlb is tied intimately to the core
architecture DMA support. In addition, ZONE_DMA cannot be disabled.

To aid debugging and catch devices not supporting DMA to memory outside
the 32-bit address space, add a kernel command line option
"swiotlb=noforce", which disables the use of bounce buffers.
If specified, trying to map memory that cannot be used with DMA will
fail, and a rate-limited warning will be printed.

Note that io_tlb_nslabs is set to 1, which is the minimal supported
value.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 21 insertions, 4 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 37babf91f2cb..922dec8fa07e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3998,10 +3998,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         it if 0 is given (See Documentation/cgroup-v1/memory.txt)
 
         swiotlb=        [ARM,IA-64,PPC,MIPS,X86]
-                        Format: { <int> | force }
+                        Format: { <int> | force | noforce }
                         <int> -- Number of I/O TLB slabs
                         force -- force using of bounce buffers even if they
                                  wouldn't be automatically used by the kernel
+                        noforce -- Never use bounce buffers (for debugging)
 
         switches=       [HW,M68k]
 
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 746ecebbd4ca..d2613536fd03 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -12,6 +12,7 @@ struct scatterlist;
 enum swiotlb_force {
         SWIOTLB_NORMAL,         /* Default - depending on HW DMA mask etc. */
         SWIOTLB_FORCE,          /* swiotlb=force */
+        SWIOTLB_NO_FORCE,       /* swiotlb=noforce */
 };
 
 extern enum swiotlb_force swiotlb_force;
diff --git a/include/trace/events/swiotlb.h b/include/trace/events/swiotlb.h
index 5e2e30a7efce..288c0c54a2b4 100644
--- a/include/trace/events/swiotlb.h
+++ b/include/trace/events/swiotlb.h
@@ -39,7 +39,8 @@ TRACE_EVENT(swiotlb_bounced,
                 __entry->size,
                 __print_symbolic(__entry->swiotlb_force,
                         { SWIOTLB_NORMAL,       "NORMAL" },
-                        { SWIOTLB_FORCE,        "FORCE" }))
+                        { SWIOTLB_FORCE,        "FORCE" },
+                        { SWIOTLB_NO_FORCE,     "NO_FORCE" }))
 );
 
 #endif /*  _TRACE_SWIOTLB_H */
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 68e8f49c7e06..ad1d2962d129 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -106,8 +106,12 @@ 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")) {
+                swiotlb_force = SWIOTLB_NO_FORCE;
+                io_tlb_nslabs = 1;
+        }
 
         return 0;
 }
@@ -541,8 +545,15 @@ static phys_addr_t
 map_single(struct device *hwdev, phys_addr_t phys, size_t size,
            enum dma_data_direction dir)
 {
-        dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
+        dma_addr_t start_dma_addr;
+
+        if (swiotlb_force == SWIOTLB_NO_FORCE) {
+                dev_warn_ratelimited(hwdev, "Cannot do DMA to address %pa\n",
+                                     &phys);
+                return SWIOTLB_MAP_ERROR;
+        }
 
+        start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
         return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size, dir);
 }
 
@@ -707,6 +718,9 @@ static void
 swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
              int do_panic)
 {
+        if (swiotlb_force == SWIOTLB_NO_FORCE)
+                return;
+
         /*
          * Ran out of IOMMU space for this operation. This is very bad.
          * Unfortunately the drivers cannot handle this operation properly.