From 6c9c6d6301287e369a754d628230fa6e50cdb74b Mon Sep 17 00:00:00 2001 From: Shuah Khan Date: Mon, 8 Oct 2012 11:08:06 -0600 Subject: dma-debug: New interfaces to debug dma mapping errors Add dma-debug interface debug_dma_mapping_error() to debug drivers that fail to check dma mapping errors on addresses returned by dma_map_single() and dma_map_page() interfaces. This interface clears a flag set by debug_dma_map_page() to indicate that dma_mapping_error() has been called by the driver. When driver does unmap, debug_dma_unmap() checks the flag and if this flag is still set, prints warning message that includes call trace that leads up to the unmap. This interface can be called from dma_mapping_error() routines to enable dma mapping error check debugging. Tested: Intel iommu and swiotlb (iommu=soft) on x86-64 with CONFIG_DMA_API_DEBUG enabled and disabled. Signed-off-by: Shuah Khan Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Joerg Roedel --- Documentation/DMA-API.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'Documentation') diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index 66bd97a95f10..78a6c569d204 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -678,3 +678,15 @@ out of dma_debug_entries. These entries are preallocated at boot. The number of preallocated entries is defined per architecture. If it is too low for you boot with 'dma_debug_entries=' to overwrite the architectural default. + +void debug_dmap_mapping_error(struct device *dev, dma_addr_t dma_addr); + +dma-debug interface debug_dma_mapping_error() to debug drivers that fail +to check dma mapping errors on addresses returned by dma_map_single() and +dma_map_page() interfaces. This interface clears a flag set by +debug_dma_map_page() to indicate that dma_mapping_error() has been called by +the driver. When driver does unmap, debug_dma_unmap() checks the flag and if +this flag is still set, prints warning message that includes call trace that +leads up to the unmap. This interface can be called from dma_mapping_error() +routines to enable dma mapping error check debugging. + -- cgit v1.2.2 From 8d7f62e6a7aa0bfd7163d3c4a5fb59280f6a6eb5 Mon Sep 17 00:00:00 2001 From: Shuah Khan Date: Thu, 18 Oct 2012 14:00:58 -0600 Subject: Documentation DMA-API-HOWTO.txt Add dma mapping error check usage examples Enhance the document to discuss the importance of dma mapping error checks after dma_map_single() and dma_map_page() calls. Also added usage examples that include unmap examples in error paths when dma mapping error is returned. Includes correct and incorrect usages to high light some common mistakes in error paths especially when dma mapping fails when more than one dma mapping call is made. Signed-off-by: Shuah Khan Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Joerg Roedel --- Documentation/DMA-API-HOWTO.txt | 126 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 126 insertions(+) (limited to 'Documentation') diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt index a0b6250add79..4a4fb295ceef 100644 --- a/Documentation/DMA-API-HOWTO.txt +++ b/Documentation/DMA-API-HOWTO.txt @@ -468,11 +468,46 @@ To map a single region, you do: size_t size = buffer->len; dma_handle = dma_map_single(dev, addr, size, direction); + if (dma_mapping_error(dma_handle)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + goto map_error_handling; + } and to unmap it: dma_unmap_single(dev, dma_handle, size, direction); +You should call dma_mapping_error() as dma_map_single() could fail and return +error. Not all dma implementations support dma_mapping_error() interface. +However, it is a good practice to call dma_mapping_error() interface, which +will invoke the generic mapping error check interface. Doing so will ensure +that the mapping code will work correctly on all dma implementations without +any dependency on the specifics of the underlying implementation. Using the +returned address without checking for errors could result in failures ranging +from panics to silent data corruption. Couple of example of incorrect ways to +check for errors that make assumptions about the underlying dma implementation +are as follows and these are applicable to dma_map_page() as well. + +Incorrect example 1: + dma_addr_t dma_handle; + + dma_handle = dma_map_single(dev, addr, size, direction); + if ((dma_handle & 0xffff != 0) || (dma_handle >= 0x1000000)) { + goto map_error; + } + +Incorrect example 2: + dma_addr_t dma_handle; + + dma_handle = dma_map_single(dev, addr, size, direction); + if (dma_handle == DMA_ERROR_CODE) { + goto map_error; + } + You should call dma_unmap_single when the DMA activity is finished, e.g. from the interrupt which told you that the DMA transfer is done. @@ -489,6 +524,14 @@ Specifically: size_t size = buffer->len; dma_handle = dma_map_page(dev, page, offset, size, direction); + if (dma_mapping_error(dma_handle)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + goto map_error_handling; + } ... @@ -496,6 +539,12 @@ Specifically: Here, "offset" means byte offset within the given page. +You should call dma_mapping_error() as dma_map_page() could fail and return +error as outlined under the dma_map_single() discussion. + +You should call dma_unmap_page when the DMA activity is finished, e.g. +from the interrupt which told you that the DMA transfer is done. + With scatterlists, you map a region gathered from several regions by: int i, count = dma_map_sg(dev, sglist, nents, direction); @@ -578,6 +627,14 @@ to use the dma_sync_*() interfaces. dma_addr_t mapping; mapping = dma_map_single(cp->dev, buffer, len, DMA_FROM_DEVICE); + if (dma_mapping_error(dma_handle)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + goto map_error_handling; + } cp->rx_buf = buffer; cp->rx_len = len; @@ -658,6 +715,75 @@ failure can be determined by: * delay and try again later or * reset driver. */ + goto map_error_handling; + } + +- unmap pages that are already mapped, when mapping error occurs in the middle + of a multiple page mapping attempt. These example are applicable to + dma_map_page() as well. + +Example 1: + dma_addr_t dma_handle1; + dma_addr_t dma_handle2; + + dma_handle1 = dma_map_single(dev, addr, size, direction); + if (dma_mapping_error(dev, dma_handle1)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + goto map_error_handling1; + } + dma_handle2 = dma_map_single(dev, addr, size, direction); + if (dma_mapping_error(dev, dma_handle2)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + goto map_error_handling2; + } + + ... + + map_error_handling2: + dma_unmap_single(dma_handle1); + map_error_handling1: + +Example 2: (if buffers are allocated a loop, unmap all mapped buffers when + mapping error is detected in the middle) + + dma_addr_t dma_addr; + dma_addr_t array[DMA_BUFFERS]; + int save_index = 0; + + for (i = 0; i < DMA_BUFFERS; i++) { + + ... + + dma_addr = dma_map_single(dev, addr, size, direction); + if (dma_mapping_error(dev, dma_addr)) { + /* + * reduce current DMA mapping usage, + * delay and try again later or + * reset driver. + */ + goto map_error_handling; + } + array[i].dma_addr = dma_addr; + save_index++; + } + + ... + + map_error_handling: + + for (i = 0; i < save_index; i++) { + + ... + + dma_unmap_single(array[i].dma_addr); } Networking drivers must call dev_kfree_skb to free the socket buffer -- cgit v1.2.2