From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Tomoya MORINAGA" Subject: Re: [PATCH net-next-2.6 v3] can: Topcliff: PCH_CAN driver: Add Flow control, Date: Thu, 25 Nov 2010 21:03:45 +0900 Message-ID: <001b01cb8c98$d06aaa00$66f8800a@maildom.okisemi.com> References: <4CE2434B.5050701@dsn.okisemi.com> <4CE27796.2000206@pengutronix.de> <007401cb87b1$a773b3d0$66f8800a@maildom.okisemi.com> <4CE64167.2030405@pengutronix.de> <003201cb8a02$f05b15e0$66f8800a@maildom.okisemi.com> <4CEA2986.4080607@pengutronix.de> <000b01cb8b6b$d7542a90$66f8800a@maildom.okisemi.com> <4CED0650.7030004@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: andrew.chih.howe.khor-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, Samuel Ortiz , margie.foster-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, yong.y.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org, kok.howg.ewe-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, joel.clark-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, qi.wang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, "David S. Miller" , Christian Pellegrin , Wolfgang Grandegger To: "Marc Kleine-Budde" Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: socketcan-core-bounces-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org Errors-To: socketcan-core-bounces-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org List-Id: netdev.vger.kernel.org On Wednesday, November 24, 2010 9:34 PM, Marc Kleine-Budde wrote : >On 11/24/2010 01:09 AM, Tomoya MORINAGA wrote: >> On Monday, November 22, 2010 5:27 PM, Marc Kleine-Budde wrote: >>>>>>> Still we have the busy waiting in the TX path. Maybe you can move the >>>>>>> waiting before accessing the if[1] and remove the busy waiting here. >>>>>> I can't understand your saying. >>>>>> For transmitting data, calling pch_can_rw_msg_obj is mandatory. >>>>> Yes, but the busy wait is not needed. It should be enough to do the >>>>> busy-waiting _before_ accessing the if[1]. >>>> >>>> Do you mean we should create other pch_can_rw_msg_obj which doesn't have busy wait ? >>> ACK, and this non busy waiting is use in the TX path. But you add a busy >>> wait only function before accessing the if[1] in the TX path. >> >> The "busy waiting" of pch_can_rw_msg_obj is for next processing accesses to Message object. >> If deleting this busy waiting, next processing can access to Message object, regardless previous transfer doesn't >> complete yet. >> Thus, I think, the "busy waiting" is necessary. > >Yes, it's necessary, but not where it is done currently. >Let me outline how I think the TX path should look like: > >pch_xmit() { > take_care_about_flow_control(); > prepare_can_frame_to_be_copied_to_tx_if(); > > /* most likely we don't have to wait here */ > wait_until_tx_if_is_ready(); > > copy_can_frame_to_tx_if(); > > /* trigger tx in hardware */ > send_tx_if_but_dont_do_busywait(); > > /* tx_if is busy now, but before we access it, we'll check tx_if is ready */ >} This Tx path also has Read-Modify-Write for MessageRAM access. Do you mean Tx path shouldn't have Read-Modify-Write ? --- Thanks, Tomoya MORINAGA OKI SEMICONDUCTOR CO., LTD.