> -----Original Message----- > From: G, Manjunath Kondaiah > Sent: Tuesday, March 02, 2010 8:34 PM > To: Shilimkar, Santosh; S, Venkatraman; Tony Lindgren; Raja, Govindraj; Greg KH; linux- > serial@xxxxxxxxxxxxxxx; linux-omap@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Kevin Hilman; Olof > Johansson > Subject: RE: [PATCH] serial: Add OMAP high-speed UART driver. > > > Santosh, > > > -----Original Message----- > > From: Shilimkar, Santosh > > Sent: Tuesday, March 02, 2010 7:34 PM > > To: G, Manjunath Kondaiah; S, Venkatraman; Tony Lindgren; > > Raja, Govindraj; Greg KH; linux-serial@xxxxxxxxxxxxxxx; > > linux-omap@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > > Kevin Hilman; Olof Johansson > > Subject: RE: [PATCH] serial: Add OMAP high-speed UART driver. > > > > <snip snip> > > > > > -- > > > > CDAC is a shadow register used for monitoring the DMA channel. > > > > I think it would be a lot > > > > simpler if omap_start_dma() always resets CDAC to 0, and the > > > > UART driver > > > > just not set it explicitly. > > > > > > This seems to be better option than exposing CDAC read/write API > > > to other drivers since user need to write '0' before > > starting any DMA > > > transfer which can be be done in omap_start_dma(). > > > > > > I am wondering how other drivers are using DMA transfer > > API's without > > > resetting CDAC to zero. > > > > > It's needed only if some one is interested in that count. > > UART seems to > > using this counter where as other driver don't. > > > > Why do you think drivers need to know about counter value ? > > Reading of non zero value(after reset to zero and enabling dma channel) > from CDAC register indicates that, DMA transfer has started and user can > rely on DMA4_CCENi and DMA4_CCFNi element and frame counters. > > If the CDAC value is zero even after starting DMA channel, indicates > error. Not necessary. The DMA can still wait for the hw sync signal and the CDAC can remain 0 if the hw sync in not received. This will be any way returned by DMA error ( SYNC lost) This register was mainly suppose to be used for debug purposes. Regards, Santosh -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
