usb_alloc_coherent(9) [centos man page]

USB_ALLOC_COHERENT(9)						   USB Core APIs					     USB_ALLOC_COHERENT(9)

NAME

       usb_alloc_coherent - allocate dma-consistent buffer for URB_NO_xxx_DMA_MAP

SYNOPSIS

       void * usb_alloc_coherent(struct usb_device * dev, size_t size, gfp_t mem_flags, dma_addr_t * dma);

ARGUMENTS

       dev
	   device the buffer will be used with

       size
	   requested buffer size

       mem_flags
	   affect whether allocation may block

       dma
	   used to return DMA address of buffer

RETURN

       Either null (indicating no buffer could be allocated), or the cpu-space pointer to a buffer that may be used to perform DMA to the
       specified device. Such cpu-space buffers are returned along with the DMA address (through the pointer provided).

NOTE

       These buffers are used with URB_NO_xxx_DMA_MAP set in urb->transfer_flags to avoid behaviors like using "DMA bounce buffers", or thrashing
       IOMMU hardware during URB completion/resubmit. The implementation varies between platforms, depending on details of how DMA will work to
       this device. Using these buffers also eliminates cacheline sharing problems on architectures where CPU caches are not DMA-coherent. On
       systems without bus-snooping caches, these buffers are uncached.

       When the buffer is no longer used, free it with usb_free_coherent.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						     USB_ALLOC_COHERENT(9)

svatophys(9r)															     svatophys(9r)

NAME

       svatophys - General: Converts a system virtual address to a physical address

SYNOPSIS

       kern_return_t svatophys(
	       vm_offset_t kern_addr,
	       vm_offset_t *phys_addr );

ARGUMENTS

       Specifies the kernel virtual address.  Specifies a pointer to the physical address to be filled in.

DESCRIPTION

       The  svatophys routine converts a system virtual address to the corresponding physical address. All address and data structure manipulation
       done within the kernel is performed using system virtual addresses.  Typically, system virtual addresses are a means  of  mapping  physical
       memory  and  I/O  space,  which often consists of device registers and DMA buffers. In contrast to this, devices are usually unaware of any
       virtual addressing and for this reason use physical addresses. You use the svatophys routine to perform this address translation.

       As an example of where you can use this address translation, a disk device driver can use DMA buffers to transfer blocks  of  data  to  the
       disk  (for  the case of a write operation). The data to be written to disk is present in system memory at a system virtual address known to
       the driver. To initiate the DMA operation, the disk driver can set up a command packet to specify a write operation to the underlying  disk
       controller  hardware.  This write command packet contains (among other things) the location of the DMA buffer as a physical address and the
       length of the buffer. Here, the driver calls the svatophys routine to translate the system virtual address of the DMA buffer to a  physical
       address in the command packet issued to the disk driver.

RETURN VALUES

       The  svatophys  routine returns the following: The address translation has been completed successfully.	Unable to perform address transla-
       tion. This value indicates that the address specified by the kern_addr argument is not a valid kernel or system virtual address.

																     svatophys(9r)