On Thu, Feb 11, 2021 at 08:38:40AM +0000, Noam Liron wrote: > Hi Greg, > > I am writing you again on the below subject, as I would like to get a "high level" opinion, and you are probably the most experienced ... > > As I wrote below, I cannot rely on the DMA mask, as some USB allocation are not affected by it. > I thought of using private DMA pool that will be allocated where I need it (at the start of physical memory). However, this means adding specific ASIC code, which is less elegant. > Do you think that's the right way? > > Thanks, > Noam > > > -----Original Message----- > From: Greg KH <greg@xxxxxxxxx> > Sent: Monday, December 28, 2020 4:19 PM > To: Noam Liron <lnoam@xxxxxxxxxxx> > Cc: linux-usb@xxxxxxxxxxxxxxx; Yuval Shaia <yshaia@xxxxxxxxxxx> > Subject: [EXT] Re: Enforce USB DMA allocations to specific range > > External Email > > ---------------------------------------------------------------------- > On Mon, Dec 28, 2020 at 01:54:41PM +0000, Noam Liron wrote: > > Hi Greg and thanks for your reply for my previous q. (Proper way to set a DMA_MASK on a USB device). > > > > I am rephrasing my questions: > > > > I am working on LK 4.14.76, on a SOC in which RAM starts at 0x200000000, and need to limit DMA buffer allocations to be at the range 0x200000000 - 0x220000000. > > This is a SoC constraint. > > Setting the controller dma_mask to 0x21FFFFFFF, didn't solve the problem, as I noticed that URB streaming DMA are first allocated by kmalloc and alike, which are not affected by the dma_mask. > > Why not get support from who ever is forcing you to use that old kernel version? You are paying them for this, right? :) > > > I plan to do the following: > > Alloc coherent memory for the HCD using 'dma_declare_coherent_memory', and use the HCD_LOCAL_MEM so the usb core is told that it must copy data into local memory if the buffers happen to be placed in regular memory. > > > > Is that the right way to deal with this case? I think that is the correct way. That's what the HCD_LOCAL_MEM flag was meant for. Alan Stern > Have you looked at how all of the existing host controller drivers do this? Why will they not "just work" properly for you as well? > What host controller driver are you using? > > thanks, > > greg k-h
