From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Ujfalusi Subject: [PATCH v2 03/14] dmaengine: doc: Add sections for per descriptor metadata support Date: Tue, 30 Jul 2019 12:34:39 +0300 Message-ID: <20190730093450.12664-4-peter.ujfalusi@ti.com> References: <20190730093450.12664-1-peter.ujfalusi@ti.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190730093450.12664-1-peter.ujfalusi@ti.com> Sender: linux-kernel-owner@vger.kernel.org To: vkoul@kernel.org, robh+dt@kernel.org, nm@ti.com, ssantosh@kernel.org Cc: dan.j.williams@intel.com, dmaengine@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, grygorii.strashko@ti.com, lokeshvutla@ti.com, t-kristo@ti.com, tony@atomide.com, j-keerthy@ti.com List-Id: devicetree@vger.kernel.org Update the provider and client documentation with details about the metadata support. Signed-off-by: Peter Ujfalusi --- Documentation/driver-api/dmaengine/client.rst | 75 +++++++++++++++++++ .../driver-api/dmaengine/provider.rst | 46 ++++++++++++ 2 files changed, 121 insertions(+) diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst index 45953f171500..d708e46b88a2 100644 --- a/Documentation/driver-api/dmaengine/client.rst +++ b/Documentation/driver-api/dmaengine/client.rst @@ -151,6 +151,81 @@ The details of these operations are: Note that callbacks will always be invoked from the DMA engines tasklet, never from interrupt context. + Optional: per descriptor metadata + --------------------------------- + DMAengine provides two ways for metadata support. + + DESC_METADATA_CLIENT + + The metadata buffer is allocated/provided by the client driver and it is + attached to the descriptor. + + .. code-block:: c + + int dmaengine_desc_attach_metadata(struct dma_async_tx_descriptor *desc, + void *data, size_t len); + + DESC_METADATA_ENGINE + + The metadata buffer is allocated/managed by the DMA driver. The client + driver can ask for the pointer, maximum size and the currently used size of + the metadata and can directly update or read it. + + .. code-block:: c + + void *dmaengine_desc_get_metadata_ptr(struct dma_async_tx_descriptor *desc, + size_t *payload_len, size_t *max_len); + + int dmaengine_desc_set_metadata_len(struct dma_async_tx_descriptor *desc, + size_t payload_len); + + Client drivers can query if a given mode is supported with: + + .. code-block:: c + + bool dmaengine_is_metadata_mode_supported(struct dma_chan *chan, + enum dma_desc_metadata_mode mode); + + Depending on the used mode client drivers must follow different flow. + + DESC_METADATA_CLIENT + + - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM: + 1. prepare the descriptor (dmaengine_prep_*) + construct the metadata in the client's buffer + 2. use dmaengine_desc_attach_metadata() to attach the buffer to the + descriptor + 3. submit the transfer + - DMA_DEV_TO_MEM: + 1. prepare the descriptor (dmaengine_prep_*) + 2. use dmaengine_desc_attach_metadata() to attach the buffer to the + descriptor + 3. submit the transfer + 4. when the transfer is completed, the metadata should be available in the + attached buffer + + DESC_METADATA_ENGINE + + - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM: + 1. prepare the descriptor (dmaengine_prep_*) + 2. use dmaengine_desc_get_metadata_ptr() to get the pointer to the + engine's metadata area + 3. update the metadata at the pointer + 4. use dmaengine_desc_set_metadata_len() to tell the DMA engine the + amount of data the client has placed into the metadata buffer + 5. submit the transfer + - DMA_DEV_TO_MEM: + 1. prepare the descriptor (dmaengine_prep_*) + 2. submit the transfer + 3. on transfer completion, use dmaengine_desc_get_metadata_ptr() to get the + pointer to the engine's metadata are + 4. Read out the metadate from the pointer + + .. note:: + + Mixed use of DESC_METADATA_CLIENT / DESC_METADATA_ENGINE is not allowed, + client drivers must use either of the modes per descriptor. + 4. Submit the transaction Once the descriptor has been prepared and the callback information diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst index dfc4486b5743..9e6d87b3c477 100644 --- a/Documentation/driver-api/dmaengine/provider.rst +++ b/Documentation/driver-api/dmaengine/provider.rst @@ -247,6 +247,52 @@ after each transfer. In case of a ring buffer, they may loop (DMA_CYCLIC). Addresses pointing to a device's register (e.g. a FIFO) are typically fixed. +Per descriptor metadata support +------------------------------- +Some data movement architecure (DMA controller and peripherals) uses metadata +associated with a transaction. The DMA controller role is to transfer the +payload and the metadata alongside. +The metadata itself is not used by the DMA engine itself, but it contains +parameters, keys, vectors, etc for peripheral or from the peripheral. + +The DMAengine framework provides a generic ways to facilitate the metadata for +descriptors. Depending on the architecture the DMA driver can implement either +or both of the methods and it is up to the client driver to choose which one +to use. + +- DESC_METADATA_CLIENT + + The metadata buffer is allocated/provided by the client driver and it is + attached (via the dmaengine_desc_attach_metadata() helper to the descriptor. + + From the DMA driver the following is expected for this mode: + - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM + The data from the provided metadata buffer should be prepared for the DMA + controller to be sent alongside of the payload data. Either by copying to a + hardware descriptor, or highly coupled packet. + - DMA_DEV_TO_MEM + On transfer completion the DMA driver must copy the metadata to the client + provided metadata buffer. + +- DESC_METADATA_ENGINE + + The metadata buffer is allocated/managed by the DMA driver. The client driver + can ask for the pointer, maximum size and the currently used size of the + metadata and can directly update or read it. dmaengine_desc_get_metadata_ptr() + and dmaengine_desc_set_metadata_len() is provided as helper functions. + + From the DMA driver the following is expected for this mode: + - get_metadata_ptr + Should return a pointer for the metadata buffer, the maximum size of the + metadata buffer and the currently used / valid (if any) bytes in the buffer. + - set_metadata_len + It is called by the clients after it have placed the metadata to the buffer + to let the DMA driver know the number of valid bytes provided. + + Note: since the client will ask for the metadata pointer in the completion + callback (in DMA_DEV_TO_MEM case) the DMA driver must ensure that the + descriptor is not freed up prior the callback is called. + Device operations ----------------- -- Peter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. 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