From 670027c507e99521d416994a18a498def9ef2ea3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Andr=C3=A9=20Fabian=20Silva=20Delgado?= Date: Sat, 22 Oct 2016 19:31:08 -0300 Subject: Linux-libre 4.8.3-gnu --- Documentation/video4linux/cx2341x/fw-dma.txt | 96 ---------------------------- 1 file changed, 96 deletions(-) delete mode 100644 Documentation/video4linux/cx2341x/fw-dma.txt (limited to 'Documentation/video4linux/cx2341x/fw-dma.txt') diff --git a/Documentation/video4linux/cx2341x/fw-dma.txt b/Documentation/video4linux/cx2341x/fw-dma.txt deleted file mode 100644 index be52b6fd1..000000000 --- a/Documentation/video4linux/cx2341x/fw-dma.txt +++ /dev/null @@ -1,96 +0,0 @@ -This page describes the structures and procedures used by the cx2341x DMA -engine. - -Introduction -============ - -The cx2341x PCI interface is busmaster capable. This means it has a DMA -engine to efficiently transfer large volumes of data between the card and main -memory without requiring help from a CPU. Like most hardware, it must operate -on contiguous physical memory. This is difficult to come by in large quantities -on virtual memory machines. - -Therefore, it also supports a technique called "scatter-gather". The card can -transfer multiple buffers in one operation. Instead of allocating one large -contiguous buffer, the driver can allocate several smaller buffers. - -In practice, I've seen the average transfer to be roughly 80K, but transfers -above 128K were not uncommon, particularly at startup. The 128K figure is -important, because that is the largest block that the kernel can normally -allocate. Even still, 128K blocks are hard to come by, so the driver writer is -urged to choose a smaller block size and learn the scatter-gather technique. - -Mailbox #10 is reserved for DMA transfer information. - -Note: the hardware expects little-endian data ('intel format'). - -Flow -==== - -This section describes, in general, the order of events when handling DMA -transfers. Detailed information follows this section. - -- The card raises the Encoder interrupt. -- The driver reads the transfer type, offset and size from Mailbox #10. -- The driver constructs the scatter-gather array from enough free dma buffers - to cover the size. -- The driver schedules the DMA transfer via the ScheduleDMAtoHost API call. -- The card raises the DMA Complete interrupt. -- The driver checks the DMA status register for any errors. -- The driver post-processes the newly transferred buffers. - -NOTE! It is possible that the Encoder and DMA Complete interrupts get raised -simultaneously. (End of the last, start of the next, etc.) - -Mailbox #10 -=========== - -The Flags, Command, Return Value and Timeout fields are ignored. - -Name: Mailbox #10 -Results[0]: Type: 0: MPEG. -Results[1]: Offset: The position relative to the card's memory space. -Results[2]: Size: The exact number of bytes to transfer. - -My speculation is that since the StartCapture API has a capture type of "RAW" -available, that the type field will have other values that correspond to YUV -and PCM data. - -Scatter-Gather Array -==================== - -The scatter-gather array is a contiguously allocated block of memory that -tells the card the source and destination of each data-block to transfer. -Card "addresses" are derived from the offset supplied by Mailbox #10. Host -addresses are the physical memory location of the target DMA buffer. - -Each S-G array element is a struct of three 32-bit words. The first word is -the source address, the second is the destination address. Both take up the -entire 32 bits. The lowest 18 bits of the third word is the transfer byte -count. The high-bit of the third word is the "last" flag. The last-flag tells -the card to raise the DMA_DONE interrupt. From hard personal experience, if -you forget to set this bit, the card will still "work" but the stream will -most likely get corrupted. - -The transfer count must be a multiple of 256. Therefore, the driver will need -to track how much data in the target buffer is valid and deal with it -accordingly. - -Array Element: - -- 32-bit Source Address -- 32-bit Destination Address -- 14-bit reserved (high bit is the last flag) -- 18-bit byte count - -DMA Transfer Status -=================== - -Register 0x0004 holds the DMA Transfer Status: - -Bit -0 read completed -1 write completed -2 DMA read error -3 DMA write error -4 Scatter-Gather array error -- cgit v1.2.3