linux-kernel - Re: Possible race condition of the rockchip

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Message-ID: <20250922-eccentric-rustling-gorilla-d2606f-mkl@pengutronix.de>
Date: Mon, 22 Sep 2025 10:50:23 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Andrea Daoud <andreadaoud6@...il.com>
Cc: Heiko Stuebner <heiko@...ech.de>, 
	Elaine Zhang <zhangqing@...k-chips.com>, kernel@...gutronix.de, linux-can@...r.kernel.org, 
	netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Alexander Shiyan <eagle.alexander923@...il.com>
Subject: Re: Possible race condition of the rockchip_canfd driver

On 20.09.2025 18:08:03, Andrea Daoud wrote:
> > On 18.09.2025 20:58:33, Andrea Daoud wrote:
> > > I'm using the rockchip_canfd driver on an RK3568. When under high bus
> > > load, I get
> > > the following logs [1] in rkcanfd_tx_tail_is_eff, and the CAN bus is unable to
> > > communicate properly under this condition. The exact cause is currently not
> > > entirely clear, and it's not reliably reproducible.
> >
> > Our customer is using a v3 silicon revision of the chip, which doesn't
> > this workaround.
> 
> Could you please let me know how to check whether my RK3568 is v2 or v3?

Alexander Shiyan (Cc'ed) reads the information from an nvmem cell:

| https://github.com/MacroGroup/barebox/blob/macro/arch/arm/boards/diasom-rk3568/board.c#L239-L257

The idea is to fixup the device tree in the bootloader depending on the
SoC revision, so that the CAN driver uses only the needed workarounds.

> > > In the logs we can spot some strange points:
> > >
> > > 1. Line 24, tx_head == tx_tail. This should have been rejected by the if
> > > (!rkcanfd_get_tx_pending) clause.
> > >
> > > 2. Line 26, the last bit of priv->tx_tail (0x0185dbb3) is 1. This means that the
> > > tx_tail should be 1, because rkcanfd_get_tx_tail is essentially mod the
> > > priv->tx_tail by two. But the printed tx_tail is 0.
> > >
> > > I believe these problems could mean that the code is suffering from some race
> > > condition. It seems that, in the whole IRQ processing chain of the driver,
> > > there's no lock protection. Maybe some IRQ happens within the execution of
> > > rkcanfd_tx_tail_is_eff, and touches the state of the tx_head and tx_tail?
> > >
> > > Could you please have a look at the code, and check if some locking is needed?
> >
> > My time for community support is currently a bit limited. I think this
> > has to wait a bit, apologies :/
> 
> No worries, I will debug myself, and hopefully send a PR if I found
> something out.

Great, I have a both a v2 and a v3 SoC here to test.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
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