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

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Date:   Wed, 10 Jun 2020 17:01:24 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Mark Brown <broonie@...nel.org>
Cc:     Pavel Machek <pavel@...x.de>,
        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 Mon 2020-06-08 12:16:19, Mark Brown wrote:
> 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.  

Aha, patch makes sense, then. Thanks for explanation!
								Pavel
-- 
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HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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