> -----Original Message----- > From: Russell King - ARM Linux [mailto:linux@xxxxxxxxxxxxxxxx] > Sent: Thursday, August 05, 2010 6:42 PM > To: Mankad, Maulik Ojas > Cc: 'Sergei Shtylyov'; Shilimkar, Santosh; linux-usb@xxxxxxxxxxxxxxx; > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; 'Felipe Balbi' > Subject: Re: [PATCH] usb: musb: host: Issue a memory barrier before > staring the DMA > > On Thu, Aug 05, 2010 at 06:24:31PM +0530, Maulik wrote: > > > > Index: omap4_integration/drivers/usb/musb/musb_host.c > > > > =================================================================== > > > > --- omap4_integration.orig/drivers/usb/musb/musb_host.c > > > > +++ omap4_integration/drivers/usb/musb/musb_host.c > > > > @@ -628,6 +628,11 @@ static bool musb_tx_dma_program(struct d > > > > u8 mode; > > > > > > > > #ifdef CONFIG_USB_INVENTRA_DMA > > > > + /* > > > > + * Ensure the data reaches to main memory before starting > > > > + * DMA transfer > > > > + */ > > > > + wmb(); > > > > > > Are you sure this is only needed for Inventra DMA? > > > > Yes. This is seen only on SMP system such as OMAP4 which uses Inventra > DMA. > > We did not see the issue when SMP is disabled. > > It'll be far safer to actually consider what's going on here, and realise > that it's NOT a SMP issue but a write ordering issue. > > What that means is that as OMAP systems progress, and the ordering becomes > weaker, you will see the problem appearing on non-SMP. So why not fix it > properly now and avoid having to revisit this with yet more patches. > > Think about what happens if writes to memory (DMA or otherwise) in the > program become mis-ordered with writes to the device registers - and fix > anything where that ordering matters by adding the necessary barriers. > This will save you having to constantly revisit the driver time and time > again to move the barriers around. This patch fixes all OMAP processors. The other architecture Da-Vinci which uses same Mentor USB controller but different DMA engine(CPPI) may need this fix but we are not sure about this. Hence only OMAP is patched. Regards, Santosh -- 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
