On Thu, Dec 15, 2022 at 11:57:17AM +0100, Ricardo Ribalda wrote: > There is no need to make a kzalloc just for 16 bytes. Let's embed the data > into the main data structure. > > Now that we are at it, lets remove all the castings and open coding of > offsets for it. > > [Christoph, do you think dma wise we are violating any non written rules? :) thanks] There _is_ a rule, and it is not exactly unwritten. The kerneldoc for the transfer_buffer member of struct urb says: This buffer must be suitable for DMA; allocate it with kmalloc() or equivalent. Which in general means that the buffer must not be part of a larger structure -- not unless the driver can guarantee that the structure will _never_ be accessed while a USB transfer to/from the buffer is taking place. There are examples all over the USB subsystem where buffers as small as one or two bytes get kmalloc'ed in order to obey this rule. 16 bytes is certainly big enough that you shouldn't worry about it being allocated separately. Alan Stern
