On Tue. 7 Jun 2022 at 18:49, Oliver Neukum <oneukum@xxxxxxxx> wrote: > On 05.06.22 15:45, Vincent MAILHOL wrote: > > > > This is how I see things: > > * In the open() function, the driver will do the coherent allocation > > for its transfer_buffers, fill those into URBs and add all the URBs in > > an anchor. > > * During runtime, the driver will keep recycling the same URBs (no > > need to kill URB nor to usb_free_coherent() the transfer_buffer). > Yes. > > * Finally, in the close() function, the driver has to kill the URBs > > and usb_free_coherent() the transfer_buffers. As far as I understand, > > no helper functions allow us to do all that, thus requiring the driver > > to iterate through the anchor to manually usb_free_coherent() the > > transfer buffer. > Yes. But you cannot nicely solve that with a flag as you proposed. You > would need to use a helper function. > > So, the intent of this patch is to provide a method to both kill the > > URBs and usb_free_coherent() the transfer buffer at once. The > Well, you don't directly. Your patch frees the buffer together with the URB. > That has some uses, but you still would need to iterate over the URBs > Yes, there is a helper for that, but then you cover one and only one > use case, that is, you leave no way to free the buffers without > at the same time discrading the URBs. > > You can do that, but it strikes me as unelegant. Elegancy is also my concern. My RFC originated from this patch: https://lore.kernel.org/linux-can/alpine.DEB.2.22.394.2206031547001.1630869@thelappy/ Here the proposed solution was to keep a pointer of all the transfer_buffer in a local array to be able to free them when closing. I really found that original patch to be unelegant which led me to propose this RFC. Comparatively, I still think my patch to be a more elegant solution, and the original author also seems to share my thoughts. If my patch is unelegant, then what would be the elegant/state of the art way to free all this DMA allocated memory? (pointing to any reference driver implementation should be enough for me to understand). Yours sincerely, Vincent Mailhol
