Vikram > -----Original Message----- > From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb- > owner@xxxxxxxxxxxxxxx] On Behalf Of Pandita, Vikram > Sent: Tuesday, December 15, 2009 9:53 PM > To: Gadiyar, Anand; Alan Stern; Matthieu CASTET > Cc: linux-usb@xxxxxxxxxxxxxxx; David Brownell > Subject: RE: gadget framework data alignment > > > > >-----Original Message----- > >From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb- > owner@xxxxxxxxxxxxxxx] On Behalf Of Gadiyar, > >Anand > >Sent: Tuesday, December 15, 2009 10:10 AM > >To: Alan Stern; Matthieu CASTET > >Cc: linux-usb@xxxxxxxxxxxxxxx; David Brownell > >Subject: RE: gadget framework data alignment > > > >Alan Stern wrote: > >> On Tue, 15 Dec 2009, Matthieu CASTET wrote: > >> > >> > Hi, > >> > > >> > > >> > I am wondering about using dma with gadget. > >> > > >> > From what I understand gadget function can put anything in req->buf. > >> > That is the case for u_ether that puts skb->data. > >> > > >> > But if the driver wants to do dma they need a buffer aligned on a > cache > >> > boundary (to clean/invalidate/flush buffer). > >> > > >> > Who should do the job ? > >> > - Gadget function should provide "provide DMA-safe buffers" like in > spi > >> > subsystem ? > >> > - Driver need to copy the data in a safe buffer. > >> > >> Buffers should be allocated by calling kmalloc() or equivalent > >> functions. These routines always return addresses that are > >> cacheline-aligned on architectures which require it. > >> > > > >For g_ether, the buffers are allocated using kmalloc(), but the > >networking code seems to move the data in the buffer out by 2 > >bytes, and passes this unaligned address down to the gadget driver. > > > >The MUSB controller in the beagleboard could handle these unaligned > >DMA address, but looks like newer MUSB controllers don't seem to > >like this. > > I would split this problem into two parts: > > RX g-ether buffers: > The offset by 2 gets taken care if we override NET_IP_ALIGN to 4. > (Refer: include/linux/skbuff.h) > Seems this macro is for this specific purpose and works, > it's a different thing where to override in code (probably in arch > specific system.h file) By overriding NET_IP_ALIGN to 4 in arch/arm/include/asm/system.h, It is impacting other things also. Such as basic Ethernet is not working. I tried the values 0 and 4 in skb_reserve for RX g_ether buffers. Both are working fine. So we should use some different macro for this purpose. > > TX g-ether buffers > Tx buffers still come unaligned by offset 2 and just changing > NET_IP_ALIGN to 4 does not help. > > > > >- Anand > >-- > >To unsubscribe from this list: send the line "unsubscribe linux-usb" in > >the body of a message to majordomo@xxxxxxxxxxxxxxx > >More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe linux-usb" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
