Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 25 Nov 2010 13:08:42 +0100 | From | Marc Kleine-Budde <> | Subject | Re: [PATCH net-next-2.6 v3] can: Topcliff: PCH_CAN driver: Add Flow control, |
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On 11/25/2010 01:03 PM, Tomoya MORINAGA wrote: > 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 ?
Why do you Read-Modify-Write for TX? Naively speaking you just need to push your Data into a Mail/IF/Whatever and push the send button.
Marc
-- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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