On 03/02/2016 11:08 AM, Ramesh Shanmugasundaram wrote: >>>> I see no locking for the tx-path. >>> >>> I am not sure why locking is needed in tx-path? >> >> If the tx-path is shared between both channels you need locking as the >> networking subsystem may send one frame to each controller at the same >> time. > > Yes. Tx completion interrupt is shared by both channels but the Tx > FIFO, echo skbs, head, tail are maintained on a per channel basis. > Yes, net subsystem can send one frame to each channel at the same > time and the tx completion interrupt handler will traverse each > channel & update per channel context accordingly. Ok. Which instruction starts the transmit? Please add a comment to the code. You stop the tx_queue after this, so your code is racy, as the interrupt might happen in between. >>> However, looking at it again, I should move the incrementing of head >>> after the "sts" handing to be apt. What do you think? >> >> With one producer (one SW instance) and one consumer (the HW) you can >> write lockless code (if the HW allows it), but with two producers it's not >> possible. > > For a channel represented as netdev, there is still one producer (one > SW instance) isn't it? net acquires lock before calling xmit. The > consumer is tx completion interrupt handler which updates per channel > attributes only. Ok - I haven't looked at the code in depth yet. Now it's clear, that just the tx interrupt is shared. > Sorry if I am annoying. I have tested this with two channels > transmitting & receiving at the same time and it works fine. If I am > missing lock, I would like to understand it thoroughly before making > the change. 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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