swiotlb: Add swiotlb=noforce debug option

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>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index be2d6d0a03a486c340c85ed7ba73c59b22a6d41f..7d5f4f4cecfa6afc22089d3bcbe9033b38ec5740 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3807,10 +3807,11 @@
                        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 71d104e4c849076337e7a6c631c824886856affc..d9c84a9cde3dd7d7a6f182d3afb3870507934cf0 100644 (file)
--- 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 5e2e30a7efce0ebded6a183aca089f2fc9d31abe..288c0c54a2b4ace63a94549c136fe255e2982089 100644 (file)
--- 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 a32dce6d5101f40850326b0d9e5b0e91eb87cbc1..9def738af4f4e56861e1096b27a29ad4acd2b3d2 100644 (file)
--- 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;
 }
@@ -543,8 +547,15 @@ static phys_addr_t
 map_single(struct device *hwdev, phys_addr_t phys, size_t size,
           enum dma_data_direction dir, unsigned long attrs)
 {
-       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, attrs);
 }
@@ -721,6 +732,9 @@ 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.