linux-kernel - Re: [PATCH net-next] net: stmmac: fix broken dma

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Date:   Fri, 8 Dec 2017 00:57:45 +0100
From:   Niklas Cassel <niklas.cassel@...s.com>
To:     Joao.Pinto@...opsys.com,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose.Abreu@...opsys.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: stmmac: fix broken dma_interrupt handling
 for multi-queues

On Thu, Dec 07, 2017 at 11:56:10PM +0100, Niklas Cassel wrote:
> Since each DMA channel can be used for rx and tx simultaneously,
> the current code should probably be rewritten so that napi_struct is
> embedded in a new struct stmmac_channel.
> That way, stmmac_poll() can call stmmac_tx_clean() on just the tx queue
> where we got the IRQ, instead of looping through all tx queues.
> This is also how the xgbe driver does it (another driver for this IP).

Did anyone at Synopsys ever try this driver with a device tree
where num tx queues != num rx queues?

I know your hardware has 8 rx queues and 8 tx queues, but
that doesn't mean that you have to enable them all.

After fixing this crash, I'm still seeing tx timeouts with multi-queue
device trees. (At Axis we usually only enable 1 tx queue and 1 rx queue).

The multi-queue code seems a bit messy.. refactoring so that napi_struct
is in a struct stmmac_channel might help you guys with overall code
readability, since this would then actually match how the hardware works.

With the xgbe driver, xgbe_one_poll disable tx+rx irqs for a specific
channel, then calls futher function only with that specific channel.

With the stmmac driver, there is no connection between napi_struct
and tx. Disable irqs for tx? stmmac_poll loops through all tx queues :)