linux-kernel - Re: [PATCH 4.19 15/28] spi: dw: use "smp_mb()" to avoid sending spi data error

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Message-ID: <20200608111619.GB4593@sirena.org.uk>
Date:   Mon, 8 Jun 2020 12:16:19 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        fengsheng <fengsheng5@...wei.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 15/28] spi: dw: use "smp_mb()" to avoid sending spi
 data error

On Sun, Jun 07, 2020 at 10:09:11PM +0200, Pavel Machek wrote:

> > Because of out-of-order execution about some CPU architecture,
> > In this debug stage we find Completing spi interrupt enable ->
> > prodrucing TXEI interrupt -> running "interrupt_transfer" function
> > will prior to set "dw->rx and dws->rx_end" data, so this patch add
> > memory barrier to enable dw->rx and dw->rx_end to be visible and
> > solve to send SPI data error.

> So, this is apparently CPU-vs-device issue...

The commit message is a bit unclear but my read had been interrupt
handler racing with sending new data rather than an ordering issue with
writes to the hardware.  

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